请认真阅读下面各题，从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
21. -What do you want to be when you grow up?
-I want to be_______ social worker. Many people are in great need of our help.
A. a B. an C. the D./
22. I think_______ can make Lily change her mind. She is a person who never gives tip easily.
A. something B. anything C. nothing D. everything
23. Jim doesn't get angry easily. He is_______ Many students like to make friends with him.
A. outgoing B. easy--going C. humorous D. energetic
24. -You should be careful when_______.
-Yes, I will. I am wondering when_______ to have a rest.
A. driving; stopping B. driving; to stop
C. to drive; stopping D. to drive; to stop
25. -How was your weekend?
-Great! It was my mother's_______ birthday. We had great fun.
A. forty B. fortieth C. the fortieth D. fourteenth
26. -Why are you standing, Cathy?
-I can't see the blackboard clearly. Two tall boys are sitting_____
