21. because 
22. when 
23. although
24. unless
25.because 
26. before 
27. as
28.  though
29. if 
30. by

21. I'm going to the bank because / since / as I need some money.

22. I made lunch after / when / as soon as I got home.

23. Although / Even though / Though it's raining, she's going for a walk in the park. 

24. Unless she finishes her homework soon, she will fail the class.

25. He decided to trust Tim because / since / as he was an honest man.

26. Before / When we went to school, she decided to investigate the situation.

27. Jennifer decided to leave Tom because / since / as he was too worried about his job.

28. Dennis bought a new jacket although / even though / though he had received one as a gift last week.

29. Brandley claims that there will be trouble if / in the case that he doesn't complete the job.

30. Janice will have finished the report by the time you receive the letter.