The city has proposed a number of water treatment and conservation projects the cost of which raises water bills high enough so that even environmentalists are beginning to raise alarms.

A.the cost of which raises water bills high enough so that

B.at a cost raising water bills so high that

C.at a cost which raises water bills high enough so

D.whose cost will raise water bills so high that

E.whose cost will raise water bills high enough so that

老师这个题的B和E有啥不同呢，一个使用介词短语修饰projects,一个是用of的定语从句，在用法上有何不同呀