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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热门试题

单项选择题

Which of the following characterizes losers

A．Losers tend to postpone enjoyment and not to discipline themselves.
B．Losers tend to restrain their love and caring.
C．Losers tend to give up some of the techniques which they develop to cope with bad experiences.
D．Losers are so afraid to try new things that they often change their plans to suit the situation.

单项选择题

Which of the following questions might the Curies NOT ask in their investigations

A．What was radiation exactly
B．What materials might have radioactivity
C．How could man avoid powerful radioactivity
D．How strong is the radioactivity of radium