三、跟踪训练：（课堂练兵）
1．My mother ___ school when she was 13 years old.
A. fell out of B. dropped out of C. drop out of school D. fall out of
2. --How much did you ___ for this pen?--20 yuan.
A. pay B. buy C. cost D. take
3.When school was over, it stopped ___.
A. raining B. rain C. to rain D to raining
4. If you want ___ healthy, you must take more exercise.
A. keeps B. to keep C. keeping D keep
