单项选择题

The main difference between natural and artificial selection is that human beings______.

A．control the direction of artificial selection
B．control the direction of natural selection
C．make new genes in artificial selection
D．make new genes in natural selection
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单项选择题
Which of the following is NOT an example of artificial selection
A．the selection by a farmer of the best milk-producing cows for breeding
B．a breeder's allowing only the fastest horses to reproduce
C．the selection for reproduction of the best egg-laying chickens by the farmer
D．an increase in the number of giraffes with long necks because of a decline in the number of low-lying plants used for feeding
单项选择题
What do people most probably believe in about a process
A．Its definition.
B．Its explanation.
C．Its examples.
D．Its main idea.
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