单项选择题

A．If they don’’t involve any risks.
B．If they produce predictable side effects.
C．When the urgent need for them arises.
D．When tests show that they are relatively safe.
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单项选择题
A．Women.B．Prisoners.C．Manual workers.D．School age children.
A．Women.
B．Prisoners.
C．Manual workers.
D．School age children.
单项选择题
A．Friends.B．A police officer and an investigator.C．Two police officers.D．A police officer and a program hostess.
A．Friends.
B．A police officer and an investigator.
C．Two police officers.
D．A police officer and a program hostess.
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