1. a number of,the number ofa 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 is increasing.学生的数量在增长。2. in front of,in the front ofin front of 范围外的前面;in the front of 范围内的前面。In the front of the room sits a boy.在这个房间前面坐着一个男孩。3. three of us,the three of usthree 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 usTom, Jack and I went to the cinema yesterday.我们三个汤姆、杰克和我昨天去看电影了。4. by bus on the busby bus 乘公交车,表手段,方式,不用冠词;on the bus