y(y^3+y^2 - y - 2 ) - ( y^2 - 2 ) x ( y^2 -y +1 ) chứng minh biểu thức sau ko phụt uộc vào biến x

27. I ……go swimming when I was young. (a. could/b. would./ c. used to/d. both b and c)

13. You ………..fly to London this evening provided you don’t mind changing planes in Paris.(must/ have to/ can/ ought to)
14. I ……….. to take advantage of this opportunity to thank for your co-operation. (would like/can/ am able to/ might)
18. ………..you please refrain from smoking while the lecture is in progress? (May/ Might/ Would/ Should)
19. I ……………… persuade him as I said.(wasn’t able to/ can’t/ mustn’t/ ought not)
20. I’m sorry to bother you while you’re working, but I …………ask you a question.(can/ had to/ must/ may)
22. We …….ensure the telegram arrives in time. (had to/ must/’d rather/ might)
23. He ……..keep his family because his wages were too low. (couldn’t/mustn’t/ can’t/ didn’t have to)
24. The sea was so rough that we …………swim. (couldn’t/can’t/won’t/wouldn’t)
25. …………make an appointment to see the doctor? (May I / Could I / Will I/ Shall I )
26. Perhaps there ………. a good program on the radio. (might be/ will be/ can be/ should be)
27. I ……go swimming when I was young. (a. could/b. would./ c. used to/d. both b and c)
28. ………..take this letter to the post office, please?(May you/ Must you/ Would you/ none of these)
29. In our family my father ………sit at the top of the table. (used to/ had to/ ought to/ must)
30 Do it as well as you ……………. (must/ will/ can/ have to)
31. I …………swim in this water: it is much too cold.(mightn’t/ mustn’t/ can’t/ don’t have to)
32. you …………… imagine my surprise when I heard the news. (can/ ought to/ will/ all of these)
33. You ______ do some work instead of sitting there reading the paper. (would rather/ ought to/ won’t/ don’t have to)
34. Be careful how you hold that jug; it ……….break easily.(may/ ought to/will/ might)
35. I’m not sure where to go for my holiday, but I ……..go to China. (should/ may/ have to/ needn’t)
36. we had free tickets, so we ……….pay to get into the concert. (didn’t have to/ 
couldn’t/mustn’t/ shouldn’t)
38.Tom ……… drive . He is too tired. (would rather/ must/ needn’t to/ ought not to)
39. Shall I clean the window today? – No, you ……. (mustn’t/ needn’t/ don’t have/ shouldn’t)

 you ……….. go now. It’s getting late.(had rather/ had better/ ought/ would rather )

25. Someone ought to repair this window.

29. I was teaching  English at 1 pm yesterday.
30 .Thu was typing a letter at 2 pm last Sunday.