请问GWD7-Q15， 关于whose的用法

GWD7-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.
   D. whose cost will
     raise water bills so high that

请问这里的"whose"是指代“projects"吗？我一直都以为”whose"只可以指代“人的”。

谢过先！

看来只好这么理解了，我前面也做到过类似的题，whose用来指代物，of which的变体。