单项选择题

Recent research into aging suggests that the body's defense mechanisms may lose the ability to distinguish what is alien.

A．insane
B．infectious
C．foreign
D．poisonous
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单项选择题
Adverse reviews in the New York press may greatly change the prospects of a new Broadway production.
A．additional
B．encouraging
C．unfavorable
D．subversive
单项选择题
In the first decades of the twentieth century, the individual gene could not be seen, but could be worked with fruitfully.
A．blindly
B．completely
C．productively
D．carefully
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