关于打点的问题...希望NN给分析下

一直也没搞懂什么地方该打点,什么地方不打点..今天碰巧有道题,希望NN给分析下

Though the law will require emissions testing of all diesel vehicles, from tractor trailers to excursion buses, it will have no effect on sport utility vehicles, almost all of which are gasoline powered, and will not be subjected to emissions-control standards as stringent as they are for diesel-powered vehicles.

A.      powered, and will not be subjected to emissions-control standards as

stringent as they are for

B.      powered, and therefore not subjected to emissions-control standards

that are as stringent as those of

C.     powered and therefore not subject to emissions-control standards

      as stringent as those for

D.     powered, which are not subject to emissions-control standards as

stringent as they are for

E.      powered and therefore they are not subject to emissions-control

standards as stringent as those of

正确答案是C，我选B

B和C有个区别就是B POWERED后面有个,想问一下一般什么时候用,什么时候不用

这道题目不选B选C是不是因为这个逗号呢?

说下我的意见，不足之处请大家指出

如果选择B，and therefore not subjected to emissions-control standards在结构上就会和it will have no effect on sport utility vehicles平行，而不是和almost all of which are gasoline 平行。

而且还可以通过比较结构判断，C选项those for 中的those是指代emissions-control standards，从这里可以判断出应该选择C

恩,楼上的有道理...