31. a number of, the number of
a number of许多，谓语动词用复数。the number of…的数目，谓语动词用单数。The number of students isincreasing.
32. in front of, in the front of
in front of范围外的前面，in the front of范围内的前面 Inthe front of the room sits a boy.
33. of the day, of a day
of the day每一天的，当时的，当代的， of a day暂时的，不长久的 a famous scientist of the day
34. three of us, the three of us
three of us我们(不止三个)中的三个，the three of us我们三个(就三个人)The three of us---Tom,Jack and I went to the cinema.
35. by bus, on the bus
by bus表手段，方式，不用冠词，on the bus表范围 They went there by bus.
36. for a moment, for the moment
for a moment 片刻，一会儿，for the moment暂时，一时 Thinking for a moment, he agreed.
37. next year, the next year
next year将来时间状语，the next year过去将来时间状语 He said he would go abroad the next year.
38. more than a year, more than one year
more than a year一年多，more than one year超过一年(两年或三年等)
39. take advice, take the(one's) advice
take advice征求意见，take the advice接受忠告 He refused to take the advice and failed again.
40. take air, take the air
take air传播，走漏，take the air到户外去，散步 We take the air every day.
