11. It may be necessary to stop__________________________(每隔…时间) in the learning process and go back to the difficult points in the lessons.

12. The mad man was put in the soft-padded cell lest he ______________(伤害自己).

13.Jean did not have time to go to the concert last night because she was_______________(忙着准备) her examination.

14. The ship’s generator broke down and the pumps____________________(不得不用手工操作) instead of mechanically.

15. Why didn’t you tell me you could me the money? I___________________________ (本来不必从银行借钱的）

11. at intervals

12. injure himself

13. busy preparing for

14. had to be operated manually

15. needn’t have borrowed it from the bank.