21 The (cost of) living has (gone up) (considerably) (the last few years).

the last few years -> in the last few years.
 22 (He) is the (best-known) author I have (never) (heard of).

never -> ever
 23 Tom (didn't drive) a car since he (had) an (accident) two (years ago). 

didn't drive -> hasn't driven
24 My father (asked) me (to pay) (much attention) to English (next year) 

much attention -> more attention
25 He (said) that he was riding (his bike) (on the way home) (now). 

now -> then
26 I (asked) him how far (was it) to the station (if) I went there (by taxi). 

was it -> it was
27 They asked me (what did happen) (last night), but I was (unable to tell) (them). 

what did happen -> what had happened
28 My family (spent) an (interested holiday) (in) Europe (last summer). 

interested holiday -> interesting holiday
 29 Children always (want) to know the (resonable) why (things) are as they (are).

reasonable -> reasons
 30 The students (laughed) (happy) when they (saw) the monkeys (eating) banana. 

happy -> happily
31 (The) number of (visitors) to the (exhibition) dropped (considerable) in thesecond week.

considerable -> considerably
 32 What is (the most) (important) thing (in) (really) life? 

really -> real
33 Harry, (alike) his colleagues, (is) trying (hard) to finish his work (early).

alike -> like
 34 Lam and (his) (friends) (often go) to the cinema to (enjoy) the new films last year.

often go -> often went
 35(The) boss laughed when the secretary (has told) him that she (really) (needed) a pay rise. 

has told -> had told
36 She (is) singing and dancing (merrily) when (the doctor) called (to see) her.

is -> was
 37 (What a pity) I have to (look at) my little brother, so I (can't go) to the cinema(tonight).

look at -> look after
 38 (What a pity) I have to (look at) my little brother, so I (can't go) to the cinema(tonight). 

look at -> look after
39 (Do) you (mind) if I turn (off) the TV? I want to watch the (news). 

off -> on
40 The (official) delagation (will) arrive (at) Geneve (next) Monday.

at -> in

21. the last few years - in the last few years

22. best- known - well-known

23. didn't drive- hasn't driven

25. now - then

26. was it - it was

27. what did happen- what had happened

28. interested holiday - interesting holiday

30. happy - happily

31. considerable - considerably

32. really - real

34. often go - went

35. has told - had told

36. is - was

37. look at - look after

39. off - on