31. a number of, the number of

　　a number of 許多，謂語動詞用復數;

　　the number of 的數目，謂語動詞用單數。例：The number of students is increasing.

　　32. in front of, in the front of

　　in front of 范圍外的前面;

　　in the front of 范圍內的前面 例：In the front of the room sits a boy.

　　33. of the day, of a day

　　of the day 每一天的，當時的，當代的，例：a famous scientist of the day;

　　of a day 暫時的，不長久的。

　　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 我們三個(就三個人)例：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，例：They went there by bus.

　　on the bus 表范圍。