字幕列表 影片播放 列印英文字幕 Hello. I'm Margot Politis. Welcome to Study English, IELTS preparation. Today we're going to look at conditional sentences. They're sentences that use 'if'. If you listen carefully, you'll be able to hear Dr Malcolm Simons talking about junk DNA, the parts of DNA that people used to think were just rubbish. Listen to the different types of sentences he uses. Under Darwinistic notions, you would think that junk would drop off under the theory of natural selection, just like species drop off if they hit ecological niches, which is incompatible with survival. If they can adapt to those niches, then those that can, survive, and those that can't, die, is the notion. If you apply that to the DNA sequence, then the coding region genes, which survive, have a function, and by the way the non-coding sequences have survived as well. So the proposition would have to be that if they're there, they've got a function. In listening to Dr Simons, you can hear that he uses a variety of sentences. This makes for much more interesting language. You should practice using sentences of different lengths and types, especially complex sentences. Today we're going to look at one of the ways you can create complex sentences using an 'if clause'. An 'if clause' is a phrase that gives a condition that's necessary for something else to happen. They're often called conditional clauses. If means when, provided that, or on condition that. There are a few basic patterns for the 'if clause'. Listen to this: If they can adapt to those niches, then those that can, survive, and those that can't, die. So the proposition would have to be that if they're there, they've got a function. If they can adapt, then those that can survive. The pattern here is: if + simple present tense verb, then …. Then introduces a clause describing the consequences. Look at the second example in the extract. If they are there, they have got a function. Notice that the then is left out in this example. Then is optional. He could have said if they are there, then they have a function. Let's look at some more. If you have a university education, then you have more opportunities. But the then is optional - you can leave it out. If you have a university education, you have more opportunities. Notice that this pattern can be reversed. You have more opportunities if you have a university education. We never include then when the pattern is reversed like this. Let's try with the example from the story. If they're there, they have a function. They have got a function, if they're there. OK, now here's the second pattern for 'if' sentences. This is for when the suggestion is less definite, or less likely. If you had a university education, then you would have more opportunities. The pattern here is: if + past tense, then + would + verb. If you had a university education, then you would have more opportunities. We use this pattern when we are talking about the future, and about something that may not be as likely to happen. Compare these 2 patterns. If you study hard, then you will pass your test. If you studied hard, then you would pass your test. In the first example, it's a bit like making a useful suggestion. The second sentence is less definite, and less polite. It suggests that the person doesn't study hard now. So that's 2 ways of making the conditional tense - how to say that one thing will happen, or might happen, if something else happens. There are other forms of the conditional tense too. If you learn them, then your English will improve! OK, now we're going to look at ways of making opposites by using prefixes. Listen to Dr Simons again. Under Darwinistic notions, you would think that junk would drop off under the theory of natural selection, just like species drop off if they hit ecological niches, which is incompatible with survival. If they can adapt to those niches, then those that can, survive, and those that can't, die, is the notion. If you apply that to the DNA sequence, then the coding region genes, which survive, have a function and by the way the non-coding sequences have survived as well. In the passage we heard the words survive and die. They have opposite meanings. 'To survive' means to keep on living and 'to die' means to stop living. We call words with opposite meanings, opposites. Sometimes opposites are formed from the same word stem using prefixes. Two of the prefixes he uses are 'in' and 'non'. Listen: And by the way the non-coding sequences have survived as well. He calls the junk DNA the non-coding sequences. Non-coding means not coding. Notice that we use a hyphen with the non- prefix. Non- usually forms adjectives. It means 'not in the group of', so we have non-European, non-Aboriginal or non-government. Non- can also just means not, giving a negative sense to a word - non-fiction, non-smoking and non-stick. The prefix 'in' is used with adjectives as well. It also makes opposites, and means 'not'. It forms words like: insignificant, not significant; inexpensive, not expensive; intolerant, not tolerant. Another common opposite prefix is un-. We can have unfair, unattractive, unusual, unnatural. But un- can also be used with verbs. It means that an action is reversed. So we have undo, undress or unbend. There aren't many rules about what sorts of words take these prefixes. You'll have to learn most opposites one by one. A good way to do this is to try to find out the opposite every time you come across a new word. Finally for today, let's have a look at how you can form adjectives from people's names. Under Darwinistic notions, you would think that junk would drop off under the theory of natural selection. He says under Darwinistic notions. Darwinistic here is an adjective, but it's got a capital letter - do you know why? Well, that's because It comes from the name 'Darwin' - referring to Charles Darwin, who developed the theory of natural selection. But it's got 2 suffixes: -ist and -ic. The -ic suffix forms adjectives that mean belonging to, or like. So 'Darwinistic' means like a Darwinist. But a 'Darwinist'? Well the suffix -ist forms adjectives too, but it forms an adjective that describes a type of person with a certain set of beliefs. When -ist is added to people's names, it means someone who follows that person, or who believes in what they wrote or said. So we can have a Darwinist, someone who believes in Darwin's theories, or a Marxist, someone who follows the writings of Marx, or a Buddhist, someone who follows the teachings of the Buddha. Well, we're out of time for today. Remember to watch out for those opposites, and try using 'if' clauses. See you next time. Bye Bye.