单项选择，从A、B、C中选出最佳的答案。
1）— Can I borrow your dictionary?
— Yes, sure, you ______ .
A. might B. will C. can
2）That tall boy ______ be John. John is medium height.
A. mustn't B. must C. can't
3）Mr. Thin was very poor, ______ he was very happy.
A. and B. but C. so
4）It's hard ______ a job.
A. to look for B. to find C. to find out