参考答案:
• 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.
• 16. shall have left for
• 17. is often a very time-consuming job
• 18. something was done/some measures were taken
• 19. overcame it/got over it
• 20. in the way