单项选择题
A.17ns B.17us C.1.7ms D.17s
A.25 B.80 C.100 D.12.5
A.4 B.2 C.1 D.3
A.4英尺,2英尺 B.5英尺,3英尺 C.1米,0.4米 D.1米,0.5米
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