It is sometimes said that the English are polite people. This can make life difficult for foreigners. Suppose a foreign boy asks an English girl to go out with him and she says. "If I finish my work, I'll meet you in the cafe at 7 o'clock." Is she saying "yes" or "no" to his invitation?
In grammatical terms, she is using the conditional structure (假设结构). By using the conditional, speakers of English can avoid giving a "yes" or "no" answer to a question. It enables people to be diplomatic(有策略). If the girl doesn't want to go out with the boy, she won't turn up at the place she will let him understand she is still working. If she wants to go out with him, but doesn't want to appear too easy to catch, she has achieved that with her reply. But in this case, as she uses the first conditional which shows probability, she is quite likely to turn up at the caf. Being polite can make life very difficult. 
The conditional is often used by people in the news-politicians, for example-who wish to avoid speaking out their ideas. This is very important if they are on their way to discuss an agreement. No one wants to give away his or her points before he or she starts. A government spokesman might say to a group of workers, "if we could pay you more, we would" .The use of the conditional here makes room for argument although the speaker is using the second conditional form, which shows improbability. So it is unlikely the workers will get their rise.
"If" is a small word, which appears often in the English language. It can show politeness and conditionals such as the First-probability-if I can come to your party, I will, the Second - improbability - if I saw you tomorrow. I'd give you the book, and the Third-impossibility(meaning it is too late to change something that has happened)-if you had told me. I would have helped you.
77.The use of conditional can make a speech________.
A.clearer     B.quicker        C.more polite      D.more exciting
78.Which of the following is TRUE according to the passage?
A.Language used in the news should make room to argue.
B.Usually English girls are not easy to catch.
C.English people never speak out their ideas in public
D.The word "if" can show different meanings.
79.In the passage, "If we could pay you more, we would." probably means________.
A.the workers make more money      B.the spokesman doesn't promise anything
C.the spokesman keeps his word        D.the workers' problems aren't difficult
80.If someone says, "If I were free now, I would go with you", he means that________.
A.he is very polite to you      B.he will go with you
C.he regrets that he didn't go with you  D.he refuses to go with you