152. When the technique known as gene-splicing was invented in the early 1970's, it was feared that scien­tists might inadvertently create an "Andromeda strain," a microbe never before seen on Earth that might escape from the laboratory and it would kill vast numbers of humans who would have no natural defenses against it.

(A) it would kill vast numbers of humans who would have no natural defenses against it

(B) it might kill vast numbers of humans with no natural defenses against it

(C) kill vast numbers of humans who would have no natural defenses against it(虚拟语气没有错)

(D) kill vast numbers of humans who have no natu­ral defenses against them

(E) kill vast numbers of humans with no natural defenses against them

请问：DE除了them使用错误以外还有别的错误吗？D中who引导的是限制型定语从句还是非限制性定语从句？

E改成kill vast numbers of humans with no natural defenses against it对吗？