单项选择题

Pollution in water is noticed______.

A．when poisons are poured into water
B．when a great many fish and birds die
C．when the first organisms are affected
D．as soon as the balance of nature is destroyed

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热门试题

单项选择题

The way to stop water pollution is______.

A．to put oxygen into the river
B．to realize the serious situation clearly
C．to make the waste materials harmless
D．to make special room in the sea for our waste

单项选择题

The living things die because there is no ______ in the river or sea.

A．oxygen
B．poison
C．water
D．fish