III.
1, A. spend
2, B. because
IV.
1, A. Unless you are careful, you will cut yourself with that knife.
2, D. If he left immediately, I wouldn't call a policeman.
3, B. If today were Sunday, the pupils could go swimming.
4, A. If you don't stop talking, you won't understand the lesson.
5, C. Unless the homework is easy, I will ask you for help.
6, C. If you promise to return the book next week, I'll let you borrow it.