Could I borrow that book when you've finished reading it?that book 是一起的,就是“那本书”的意思整句话意思是：当你已经读完那本书的时候我能借一下么?you've finished reading it 就是明显的一个现在完成时啊...you've finished reading 现在完成进行时吗？那reading是动名词?呵呵。不是的 have done sth这里的have已经跟了finished了呀。然后finish+doing的结构所以变成了have finished doing sth 啊再举个例子 I have decided to go to USA.这里have decided 已经符合have done 的语法了、然后decide+to do sth综合就变成了have decided to do sth 了、还有什么词+doing的结构？好多的。一时也说不过来你初中的吧？多看书。很多句型书里课文里很明显可以找到！有些词doing 也可以 to do 也可以 但用法不同