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IELTS Preparation Series 2, Episode 8: Air Archive

September 4, 2016

 

(Bấm vào đây để chọn bài học kế tiếp)

 

Xem lời thoại bên dưới:

 

0:13

Hello. I'm Margot Politis. Welcome to Study English, IELTS preparation.

0:18

Today we're taking a look at tenses. We'll focus on the present perfect and simple past

0:25

tenses, and we'll hear examples of each.

0:29

Then, we'll practice using some adverbs of time.

0:32

The clip we're looking at today is about greenhouse gases. Scientists have been measuring the

0:39

concentration of certain gases, stored in ice in Antarctica. Let's find out more.

0:49

The air archived in ice helps prove how much the level of greenhouse gases in the atmosphere

0:54

has changed in just the last two hundred years.

1:00

What we've found out is that indeed there were much lower concentrations pre-industrially,

1:04

around about a third of the methane concentration that we have presently. We've seen a big increase

1:11

in carbon dioxide, so the two main greenhouse gases in the atmosphere have increased.

1:17

If you look back a half a million years ago, we don't see concentrations anything like

1:24

we have presently. We can link those high concentrations of the present day uniquely

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to activities of man - combusting of fossil fuels, clearing of lands and so on, agricultural

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activities.

1:35

As you know, there is a variety of verb tenses in English - simple, perfect and continuous.

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Tenses are used to describe 'past', 'present' and 'future' actions.

1:51

Sometimes, we need to give more information about when an action happened, how long it

1:56

happened for and whether it is continuing.

2:01

When an action has been completed, we use the present perfect tense.

2:06

Listen to Dr Etheridge use it here.

2:11

What we've found out is that indeed there were much lower concentrations pre-industrially,

2:12

around about a third of the methane concentration that we have presently. We've seen a big increase

2:21

in carbon dioxide, so the two main greenhouse gases in the atmosphere have increased.

2:27

Dr Etheridge uses the present perfect tense.

2:31

He says: 'we've found out'

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He's talking about an action that has been completed.

2:40

He also says: 'we've seen', and

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'greenhouse gases have increased'.

2:48

These actions started sometime in the past but have now been completed - they are in

2:54

the present perfect tense.

2:58

When an action has only recently been completed, we can highlight this by using the adverb

3:04

'just'.

3:05

Listen to the reporter.

3:08

The air archived in ice helps prove how much the level of greenhouse gases in the atmosphere

3:14

has changed in just the last two hundred years.

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She says that: "The level of greenhouse gases has changed in 'just' the last two hundred

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years".

3:27

By using the word 'just', she is telling us that two hundred years isn't very long in

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geological time. It's only 'just' happened.

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She's also using the present perfect tense.

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Let's have a look at how we structure the present perfect tense.

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We use the auxiliary verb 'to have' and a past participle.

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So here's our auxiliary verb:

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to have - I have, you have, she has, we have, they have

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And then a past participle - for example:

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changed, found out, seen, increased

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or helped.

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So we have:

4:25

I have changed

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you have found out

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she has seen

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we have increased

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they have helped

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Now let's take a look at the simple past tense.

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We use the simple past tense when an action occurs at a particular time in the past.

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For example:

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last Christmas or

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on the 15th of May or

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in 1979, or

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three million years ago.

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Let's listen to Dr Etheridge.

5:09

What we've found out is that indeed there were much lower concentrations pre-industrially,

5:13

around about a third of the methane concentration that we have presently.

5:20

He says that: "There were much lower concentrations pre-industrially."

5:24

This refers to a particular time in the past - that is, 'pre-industrially' or 'before the

5:33

industrial revolution' in Europe.

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The atmosphere was cleaner then because there weren't industries producing greenhouse gases

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and other pollution.

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So, the simple past tense describes an action that occurred at 'a specific time' in the

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past.

5:50

But the present perfect tense describes an action that has been completed at 'some indefinite

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time' in the past.

6:05

We've already seen how the reporter uses the adverb 'just'. 'Just' is an adverb of time.

6:14

There are several adverbs of time. They can be used with the present perfect tense to

6:19

give a number of different meanings.

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Listen again.

6:24

The air archived in ice helps prove how much the level of greenhouse gases in the atmosphere

6:30

has changed in just the last two hundred years.

6:34

The reporter uses the adverb 'just'.

6:38

When you are using the present perfect to talk about a recently completed action, you

6:43

can use the adverbs 'just', 'already', 'yet' or 'still'.

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For example:

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The level has changed in 'just' two hundred years.

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The Earth's atmosphere has 'already' been destroyed.

7:00

The adverbs of time 'yet' and 'still' are used in question forms and negative constructions.

7:09

For example:

7:10

Have you finished your assignment yet? No. I am still writing the introduction.

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Or: Have you finished your assignment yet? No I haven't written the introduction yet.

7:27

When we're using the present perfect tense to talk about an action that took place at

7:32

some 'indefinite time' in the past, we can use the adverbs of time 'ever' and 'never'.

7:39

'Ever' is often used in questions. It means 'has the thing been done at any time in the

7:48

past'.

7:49

Some examples are:

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Have you ever been to China?

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No, I've never been there.

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Finally, when we're talking about an action that took place at a point in the past, up

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to and including now, we can use the adverbs of time 'for' 'from' and 'since'.

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For example:

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I have been at this school for three months, since March.

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So you can see that there are different adverbs of time for different uses of the present

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perfect.

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The present perfect is a difficult tense to learn.

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It's used in statements about actions that began in the past and are still true now.

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But it can take a lot of practice to get right.

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Using adverbs of time can be useful because they help to clarify the precise use of the

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tense.

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Practice using adverbs of time, and you'll find making the right choice becomes much

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easier.

9:00

And that's all for Study English today.

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Let's review what we've done.

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We've looked at the simple past tense, and the present perfect tense.

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And then we talked about using adverbs of time in these present perfect constructions.

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Don't forget that you'll find more on these topics on our website. It's at abcasiapacific.com/studyenglish.

9:29

You'll find all the Study English stories, transcripts, study notes and much more.

9:35

And I'll see you next time. Bye bye.

 

 

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