Choose the word or set of words that, when inserted in the sentence, best fits the meaning ofthe sentence as a whole.

Scientists have discovered that our sense of smell is surprisingly ------- , capable of distinguishing thousands of chemical odors.

(A) rigid
(B) inert
(C) erratic
(D) keen
(E) innate

来源:可可英语 http://www.kekenet.com/sat/201410/333239.shtml