31. a number of, the number of??
a number of 指“許多”，謂語動詞用復(fù)數(shù)。the number of 指“…的數(shù)目”，謂語動詞用單數(shù)。如：The number of students is increasing.??????
32. in front of, in the front of??
in front of 指范圍外的前面，in the front of 指范圍內(nèi)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、當(dāng)時的、當(dāng)代的，of a day 指暫時的、不長久的，如：a famous scientist of the day。
34. three of us, the three of us??
three of us 我們（不止三個）中的三個，the three of us 我們?nèi)齻€（就三個人）。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，不用冠詞；on the bus 表范圍。如：They went there by bus.??????
36. for a moment, for the moment??
for a moment “片刻、一會兒”，for the moment“暫時、一時”，如：Thinking for a moment, he agreed.??????
37. next year, the next year??
next year 將來時間狀語，the next year 過去將來時間狀語，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“超過一年”（兩年或三年等）????
39. take advice, take the(one’s) advice??
take advice“征求意見”，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“傳播、走漏”，take the air“到戶外去、散步”，如：We take the air every day.??????
41. in a word, in words??
in a word“總之、一句話”， in words“口頭上”，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”，一般用作狀語；in the secret 指知道內(nèi)情、知道秘密，一般用作表語。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 指一個女孩，如：Can one girl carry such a big box?
45. take a chair, take the chair??
take a chair“相當(dāng)于”，sit down“坐下”，take the chair“開始開會”
46. go to sea, by sea, by the sea??
go to sea“當(dāng)海員、出航”，by sea“乘船、由海路”， by the sea“在海邊”，如：go by sea。?????
47. the doctor and teacher, the doctor and the teacher??
the doctor and teacher 指一個人，既是醫(yī)生又是老師；the doctor and the teacher 指兩個人，一個醫(yī)生和一個老師。?
48. in office, in the office??
in office“在職的”，in the office“在辦公室里”，如：He is in office, not out of office.??????
49. in bed, on the bed??
in bed“臥在床上”，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、負(fù)責(zé)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.