（1）    
GWD-7-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.

1. the
        cost of which raises water bills high enough so that
2. at
        a cost raising water bills so high that
3. at
        a cost which raises water bills high enough so
4. whose
        cost will raise water bills so high that
5. whose
        cost will raise water bills high enough so that

"whose这个代词可以修饰project吗？ 我一直认为它只能修饰
有生命的物体。"是表示从属关系都可以用吗？