单项选择题
A.30kg/m2 B.30MN/m2 C.30N/m2 D.30N/cm2
A.0.3 B.0.4 C.0.5 D.0.6
A.+100mm,-50mm B.±50mm C.+50mm D.-50mm
A.10 B.30 C.50 D.100
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