单项选择题
A.300mm B.500mm C.1000mm D.1200mm
A.1.4×107 B.7×105 C.2.4×105 D.1.3×105
A.110m B.105m C.100m D.90m
A.0.496μs B.0.491μs C.0.490μs D.0.489μs
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