The flu is believed _____by viruses that like to reproduce in the cells inside the human nose and throat.
____ him so far, she felt a little worried.
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.
My sister ,as well as her classmates who _____late for class,_____criticized by Mr. Hunt.
After five hours’ drive, they reached _____they thought was the place they had been dreaming of.
The human body consists of organs, each ____a definite job to do.