及物动词和不及物动词词汇书在讲“concentrate”时说,它当“集中”讲时是不及物动词,所以要和介词on搭配,如：concentrateonthemainissue.后来它又讲“center”.center当“集中”讲时是及物动词,那

Question

及物动词和不及物动词
词汇书在讲“concentrate”时说,它当“集中”讲时是不及物动词,所以要和介词on搭配,如：concentrate on the main issue.后来它又讲“center”.center当“集中”讲时是及物动词,那为什么它后面也要加介词on?书上举的例子：center on the main issue.我知道center可以做不及物动词,但当“集中”讲时,却是及物动词啊.

Answer 1

concentrate on
专心于,把思想集中于
Many firms are concentrating on increasing their markets overseas.
许多公司正在集中精力开拓它们的海外市场.
将…集中于…
We must concentrate our efforts on finding ways to reduce costs.
我们要集中精力找出降低成本的办法.
center on
以…为中心
The village centered on its market square.
村子中央是集市广场.
重点在于…; 主要与…有关
All his attention has centered on that experiment.
他的全部注意力都集中在那个实验上.