Part or all of the following sentence is underlined;beneath the sentence are five ways of phrasing the underlined material.Select the option that produces the best sentence.If you think the original phrasing produces a better sentence than any of the alternatives,select choice A.

Although biologists have made tremendous progress in mapping the human genome, the genetic roots of most common diseases remained largely elusive.

(A) remained
(B) had remained
(C) remain
(D) are remaining
(E) remains

来源:可可英语 http://www.kekenet.com/sat/201405/296413.shtml