请教GWD 25-37

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

powed后加了逗号，说明是插入语，所以可以去掉不影响句子成分，那么and  will  not的主语就是I（人），明显错误。。后面的they到没有歧义，但是they的话，但是指代的是standards，但是they指代就是那个东西就不对了。

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

that are as stringent as those of

同样的原因。。。插入语。。those of用的最好了。。

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

stringent as those for  正确。。但是我觉得这里的for改为of最好

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

stringent as they are for

they错误，which用法不当。。在怎么插入语，which还是就近指代。。而且前面是powed大错特错。

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

standards as stringent as those of

and主语相同，省略。。

C the best    

请问B的问题在哪里？subject不应该用被动吗

万分感谢