While other scientists are keeping eye on changes in the H5N1 bird flu strain, t

 While other scientists are keeping__ __eye onchanges in the H5N1 bird flu strain, the scientists in England are working onvaccines, in case it becomes highly infectious in __ __humans.

  A. a , /       B.an, /        C. the, an         D. an, the

试题答案

【答案】

B

【解析】这题考查冠词的用法：第一空填an，词组：keep aneye on“密切关注”，第二空不填，是泛指“人类”。选B