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
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
B