三道高一英语选择题,谢谢了1.I had a lot of trouble _____the book you want

三道高一英语选择题,谢谢了
1.I had a lot of trouble _____the book you wanted.
A.in finding
B.on finding
C.to find
D.at finding
2.After the job was finished,the builder ________the number of men working for him.
A.cut in
B.cut off
C.cut back
D.cut away
这四个选项分别是什么意思啊
3.--English has a large vocabulary,isn't it?
--Yes.________more words and expressions,and you will find it easier to read and communicate.
A.Know
B.Knowing
C.To know
D.Known
第三题讲下理由,谢谢