31. a number of, the number of  
a number of 指“许多”，谓语动词用复数。the number of 指“…的数目”，谓语动词用单数。如：The number of students is increasing.      
32. in front of, in the front of  
in front of 指范围外的前面，in the front of 指范围内的前面，如：In the front of the room sits a boy.      
33. of the day, of a day  
of the day 指每一天的、当时的、当代的，of a day 指暂时的、不长久的，如：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）。如：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。如：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”，如：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，如：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”，如：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”，如：We take the air every day.      
41. in a word, in words  
in a word“总之、一句话”， in words“口头上”，如：In a word, you are right.      
42. in place of, in the place of  
in place of“代替”，in the place of“在…地方”，如：A new building is built in the place of the old one.      
43. in secret, in the secret  
in secret“秘密地、暗自地、偷偷地”，一般用作状语；in the secret 指知道内情、知道秘密，一般用作表语。如：My mother was in the secret from t
he beginning.      
44. a girl, one girl  
a girl 可泛指所有女孩, one girl 指一个女孩，如：Can one girl carry such a big box?
45. take a chair, take the chair  
take a chair“相当于”，sit down“坐下”，take the chair“开始开会”
46. go to sea, by sea, by the sea  
go to sea“当海员、出航”，by sea“乘船、由海路”， by the sea“在海边”，如：go by sea。     
47. the doctor and teacher, the doctor and the teacher  
the doctor and teacher 指一个人，既是医生又是老师；the doctor and the teacher 指两个人，一个医生和一个老师。 
48. in office, in the office  
in office“在职的”，in the office“在办公室里”，如：He is in office, not out of office.      
49. in bed, on the bed  
in bed“卧在床上”，on the bed“在床上”，如：The book is on the bed. He is ill in bed.      
50. in charge of, in the charge of  
in charge of“管理、负责照料”，in the charge of“由……照料”，如：He is in charge of the matter. The matter is in the charge of her.