问题
选择题
While other scientists are keeping____eye on changes in the H5N1 bird flu strain, the scientists in England are working on vaccines, in case it becomes highly infectious in ____humans.
A．a , /
B．an, /
C．the, an
D．an, the
答案
答案：B
考查冠词。句意“其它科学家正在密切观察H5N1流感病毒的变化，而英国的科学家正在致力于疫苗的研究，以防止出现病毒演变成对人类具有高传染性的危险。”keep an eye on sth.“注视......”；humans“人类”，前不用冠词。故选B。