22. I didn' t manage to do it _____ you had explained how.

A. until　　　　　　　　 B. unless　　　　 　　　 C. when　　　　　　　　 D. before

21. We'd better hurry ______ it is getting dark.

A. and　　　　 　　 B. but　　　　　　　　　 C. as　　　　　　　　　　 D. unless

20. When you read the book, you' d better make a mark _____ you have any questions.

A. at which　　 　　 B. at where　　　　　　 C. the place　　　　　 D. where

19. You'll miss the train ______ you hurry up.

A. unless　　　　 B. as　　　　　　　　　　 C. if　　　　　　　 　　　 D. until

18. Speak to him slowly _____ he may understand you better.

A. since　　　　 B. so that　　　　 　　　 C. for　　　　　　　　　　 D. because

17. Although it's raining, _____ are still working in the field.

A. they　　　　　 　　　 B. but they　　　　　　 C. and they　　　　　　 D. so they

16. I'll stay here _____ everyone else comes back.

A. even if　　　　 　　　 B. as though　　　　　 C. because　　　　　　 D. until

15. We didn’t go home _____ we finished the work.

A. since　　　　 B. until　　　　　　　　 C. because　　　　　　 D. though

14. She was _____ tired _____ she could not move an inch.

A. so, that　　　 B. such, that　　　　　 C. very, that　　　　　 D. so, as

13. _____ the rain stops, we' 11 set off for the station.

A. Before 　　　　　　 B. Unless　　　　 　　　 C. As soon as　 　　　 D. Though