1 (used as the subject or object of a verb, or after a preposition) the animal or thing mentioned earlier （用作动词的主语、宾语，或放在介词后面）它: Look at that car. It's going much too fast. 瞧那辆汽车，它开得太快了。The children went up to the dog and patted it. 小孩走到那只狗的身旁，用手轻拍它。 It can also refer to a baby whose sex you do not know Is it a boy or a girl? 如果不知道婴儿的性别，也可以用it：Is it a boy or a girl?是男娃娃还是女娃娃？

2 used for identifying a person （用于指出某人身分）: It's your Mum on the phone. 是你妈妈来电话。‘Who's that?’ ‘It's the postman.’ “是谁？”“是邮递员。”It's me! 是我！It's him! 是他！

3 used in the position of the subject or object of a verb when the real subject or object is at the end of the sentence （用作动词的主语或宾语，而真正的主语或宾语在句末）: It's hard for them to talk about their problems. 要他们谈自身的问题并不容易。I think it doesn't really matter what time we arrive. 依我看，我们在什么时候到达并不重要。

4 used in the position of the subject of a verb when you are talking about time, the date, distance, the weather, etc （用作动词的主语，表示时间、日期、距离或天气等）: It's nearly half past eight. 快到八点半了。It's Tuesday today. 今天是星期二。It's about 100 kilometres from London. 离伦敦约100公里。It was very cold at the weekend. 上周末很冷。It's raining. 下着雨呢。

5 used when you are talking about a situation （指某情况）: It gets very crowded here in the summer. 这儿一到夏天就人山人海。I'll come at 7 o'clock if it's convenient. 方便的话，我7点钟来。It's a pity they can't come to the party. 真遗憾，他们来不了这个聚会。

6 used for emphasizing a part of a sentence （用于强调句子的某一部份）: It was Jerry who said it, not me. 这话是杰里说的，不是我说的。It's your health I'm worried about, not the cost. 我担心的是你的健康，不是费用。

1 that/this is the answer 对了: That's it! You've solved the puzzle! 对了！这个谜语你猜对了！

2 that/this is the end 到此为止: That's it, I've had enough! I'm going home! 好了，我受够了！我要回家了！