单项选择题
A.1Kg/cm2 B.2Kg/cm2 C.5Kg/cm2 D.10Kg/cm2
A.0.5% B.0.2% C.1% D.2%
A.大于70% B.大于60% C.大于50% D.大于80%
A.增大 B.先增大后减小 C.减小 D.不变
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