18.B

19.C

20.A

III.

1.so

2.because

3.but

4.however

5.and

6.therefore

7.because

8.but

9.or

10.so

IV.

1.Because of his hard life , he left school

2.Because John worked hard and methodically , he succeed in his exam

3.Because it rained heavily , we didn't want to go out

4.Despite his much experience in machinery , he didn't succeed in repairing this machine.

5.Though it was darkness , they continued to work

6.Because of the bad driving conditions , we postponed our trip

7.Because of it pollutions , the water of most rivers is unsafe to drink

8.Because our parents are genorous , we all have received the best of everything

18. B

19. C

20. A

III

1. so

2. because

3. although

4. but

5. to

6. so

7. because

8. but

9. or

10. so

IV

1. Because of being very poor, he coudn't go to school

2. Because of working hard and methodical, John succeeded in his exam

3. Because it rained heavily, we didn't want to go out

4. Despite his experience in machinery, he didn't succeed in repairing this machine

5. Though it dark, they continued to work

6. Because of the bad driving conditions , we postponed our trip

7. Because of its pollution, the water in most rivers is unsafe to drink

8. Because our parents are generous, we all have recieved the best of everything