121. Here are some of the rules copied from a grammar book to help those students who have difficulty in learning English.

19. I feel so grateful for your kindness. ________

18. Do you think we＇ve met before? ________

17. The boss told his secretary to ____ the documents for later use.

16. The police have not ____ the search even if it has lasted for a week.

15. Time _____ very fast and a new year will begin soon.

14. _____ a wonderful trip he had when he traveled in China!

13. She gave up her ______ as a reporter at the age of 25.

12. This new style of sports shoes is very popular and it is _____ in all sizes.

11. If there were no water in the world, everything________.

10.Ten minutes earlier, they ________the plane.