The environmental problems in China may worsen if __________ unsolved.

_______ is known to us all that the old scientist, for _______ life was hard in the past, still works hard in his eighties. 

It was dark and he had already lost his ________of direction.

The government has handed out all the ______ food and clothes to the victims.

The poet ______described the peaceful Rocky Mountain and the beautiful Mississippi River in his newly-published poetry.