Unit 4重点句子解析
1. I haven’t decided which one to write yet.
句中的which one to write是“疑问词 + 不定式”结构用在动词decide后作宾语。不定式可以与疑问词 who, what, which, when, how, where 等连用，构成不定式短语，在句中作主语、表语、宾语或宾语补足语等。如：
Where to buy this kind of computer is a problem. 到哪里去买这种计算机是一个问题。
I really don’t know what to do. 我的确不知道该怎么办了。
The question is how to get there. 问题是怎么到那里去。
Can you tell me which one to choose? 你能告诉我该选择哪一个吗？
2. If you think about it, it can take a long time to come up with the right words.
这句话中的if you think about it是条件状语从句，表示前提，短语think about意为“考虑”；第二个it是形式主语，动词take表示“花费”，真正的主语是后面的不定式to come up with the right words，短语come up with意为“想出”。如：
We don’t believe they can keep up with us. 我相信他们是不会赶上我们的。
