8. that/which　 9. As　 10. importance

5. Besides　 6. who　 7. However

1. each/every　　 2. that　 3. have used/have been using　 4. longest

1-10　 DAABB　 ABDAC

11-20 CCBCB　 BCDBC

8. Not to be noticed, he sat at the back of the room.

7. In case of danger, raise the electric alarm.

6. There is so rapid an increase in population that a food shortage is caused.

5．They are likely to become angry with him.

4．He came in quietly in order not to wake the child up.

3．He was addicted to cocaine.