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．His father caught a serious disease.B．His mother passed away.C．His mother left him to marry a rich businessman.D．His father took to drinking.
A．His father caught a serious disease.
B．His mother passed away.
C．His mother left him to marry a rich businessman.
D．His father took to drinking.
单项选择题
A．One student received a higher grade than he did.B．He will have to take a number of exams later.C．The test is more difficult than he expected.D．Several students in his class have received top grade.
A．One student received a higher grade than he did.
B．He will have to take a number of exams later.
C．The test is more difficult than he expected.
D．Several students in his class have received top grade.
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