7.D As a result of the ground-breaking work of Barbara McClintock, many scientists now believe that all of the information encoded in 50,000 to 100,000 of the different genes found in a human cell are contained in merely three percent of the cell’s DNA.

(A) 50,000 to 100,000 of the different genes found in a human cell are contained in merely

(B) 50,000 to 100,000 of the human cell’s different genes are contained in a mere

(C) the 50,000 to 100,000 different genes found in human cells are contained in merely

(D) 50,000 to 100,000 of human cell’s different genes is contained in merely（E）

(E) the 50,000 to 100,000 different genes found in a human cell is contained in a mere

E是不是太麻烦了，为什么不用D，简单些不是更好吗？

Choice B, the best answer, correctly and idiomatically uses the preposition like to introduce a comparison that is expressed, in a prepositional phrase. In A, as is used unidiomatically; in comparison, as is properly employed as a conjunction introducing a subordinate clause. Choices C, D, and E are all faulty because the verb do suggests that the migrating pearls are presented as a real phenomenon, not as a figurative illustration. Also, in D, like is used ungrammatically to introduce a subordinate clause (pearls do...); and in E, the phrase some other one, substituted for another, is awkward and wordy.

另外的一个理由是，E中的 "the cell's DNA."中的"the"是定冠词，表明CELL

前面被提到过，所以E中的 in a human cell 中的 "a"为后来的the作了铺垫。