1. Since chromosome damage may be caused by viral infections, medical x-rays, and exposure to sunlight, it is important that the chromosomes of a population to be tested for chemically induced damage be compared with those of a control population.

(A) to be tested for chemically induced damage be compared with

(B) being tested for damage induced chemically are compared with

(C) being tested for chemically induced damage should be compared to

(D) being tested for chemically induced damage are to be compared to（A）

(E) that is to be tested for chemically induced damage are to be comparable with

以前好象看懂过，现在怎么又不明白了，为什么要用虚拟语气？

碰到了同样的问题

以前只遇到过“建议、命令和要求”的动词后所接宾语从句需用虚拟语气，但是这里……

是不是只要It is adj that...这类表示强调的句子都要使用虚拟语气呀？