单项选择题

Professor James used student volunteers as ______ for his experiment.

A．models
B．cases
C．agents
D．subjects
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单项选择题
A terrible traffic accident happened; people were saddened when they watched the ______ victims.
A．panic
B．patriotic
C．pathetic
D．periodic
单项选择题
It was last year when the boy was affected with chicken pox. He should be ______ to it now.
A．subject
B．implicit
C．immune
D．stern
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