At the beginning of class, the noise of desks __________ could be heard outside the classroom.
The drug used to treat this disease causes bad side effects, some of which ________ deadly.
.No sooner ________ down on bed ________ the telephone rang.
________ about wild plants that they decided to make a trip to Madagascar for further research.
Fighting an artificial greenhouse effect seems to be the greatest of environmental challenges, ________?
A series of stimulus policies and supportive measures taken by the government ________ to promote change in the economic environment in this area.