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

What is the meaning of the underlined word waterproof in the third paragraph

A．Covered with water.
B．Full of water.
C．Cleaned by water.
D．Not allowing water to go through.

单项选择题

According to the passage, which of the following inferences is possibly true

A．Small animals have less skin for their body weight than large ones.
B．The humming-bird lives faster than any other warm blooded animals.
C．There is no limit to how large a warm blooded animal can be.
D．The humming-bird is the smallest of the warm blooded animals.