It is clear that the whole world is passing through a social revolution in which a central _____ must be taken by scientists and technologists.
The doctor recommended that you swim after eating a large meal. A wouldn't B couldn't C needn't D shouldn't
The good thing about children is that they _______ very easily to new environments.
It took ______ building supplies to construct these energy-saving houses. It took brains, too.
Over the past decades, sea ice _____ in the Arctic as a result of global warming.
The medicine works more effectively ______ you drink some hot water after taking it.