- used to refer to a thing previously mentioned or easily identified用于指已经提到的或易于确认的事物 ：
a room with two beds in it
一间有两张床的房间
this approach is refreshing because it breaks down barriers.
这种方法扫除了重重障碍, 所以让人耳目一新。
- referring to an animal or child of unspecified sex指性别不计或不详时的动物或小孩它, 这, 那：
she was holding the baby, cradling it and smiling into its face.
她抱着婴儿, 一边轻摇着它, 一边冲着它微笑。
- referring to a fact or situation previously mentioned, known, or happening刚刚提到的、已知的或正发生的事实或情形：
stop it, you're hurting me.
快停下来, 你把我弄痛了。
- used to identify a person［用于确定一个人的身份］ ：
it's me
是我
it's a boy!
是个男孩！
- used in the normal subject position in statements about time, distance, or weather［作句子主语表示时间、距离或天气等］ ：
it's half past five
五点半了
it was two miles to the island
距离小岛有两英里远
it is raining.
正在下雨。
- used in the normal subject or object position when a more specific subject or object is given later in the sentence［作先行主语或宾语, 代表句内稍后出现的更为具体的主语或宾语］ ：
it is impossible to assess the problem
无法评定这个问题
she found it interesting to learn about their strategy.
她觉得学习他们的策略很有意思。
- with clause used to emphasize a following part of a sentence［用于强调其后的句子成分］ ：
it is the child who is the victim.
这孩子才是牺牲品。
- the situation or circumstances; things in general环境; 情况, 局势：
no one can stay here - it's too dangerous now
没人能待在这个地方——现在局势太危险了
he would like to see you straight away if it's convenient.
如果方便的话, 他想马上见到你。
- exactly what is needed or desired正是所需（要或想望）的事物：
they thought they were it
他们认为自己是最棒的
you've either got it or you haven't.
要么你已得到了你想要的, 要么还没有。
- （一般作'it'）informal sexual intercourse or sex appeal〈非正式〉性交; 性欲：
the only thing I knew nothing about was 'it'.
我唯一对之一无所知的便是“性”。
- （一般作'it'）(in children's games) the player who has to catch the others（儿童游戏中的）捉人者, 找人者。
at it
- 见AT1.
that's it
- that is the main point or difficulty那正是要点; 那正是问题所在：
'Is she going?' 'That's just it - she can't make up her mind.'
“她去吗？”“那正是问题所在——她拿不定主意。”
- that is enough or the end够了; 好了：
okay, that's it, you've cried long enough.
好了, 你已经哭得够久的了。
this is it
- the expected event is about to happen（盼望的事情）即将发生; 即将来临：
this is it - the big sale.
快了——就要大甩卖了。
- this is enough or the end够了; 好了：
this is it, I'm going.
好了, 我要走了。
- this is the main point or difficulty这正是要点; 这正是问题所在。