这题真的不明白，望各位指教gwd-7-15

mmfoolish

这题选D没问题，但是B为何不对呢？偶就选了B,望各位指教！！！

Q15:

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.

the cost of which raises water bills high enough so that

at a cost raising water bills so high that

at a cost which raises water bills high enough so

whose cost will raise water bills so high that

whose cost will raise water bills high enough so that

Avantasia

BD逻辑意思不同，B的at结构更像是伴随主句主语，即proposed，意思上面说政府提出一个议案，伴随一个成本；但是D用whose，明确说明是议案本身的成本，这于A吻合。

shocking

B, D的区别主要是时态，B的意思是水费已经提高了，而D的意思是水费将要提高，显然D更符合句子的原意，因为water treatment and conservation projects刚刚被proposed(提议），还没有被执行(implemented)，所以还不会导致水费提高。