单项选择题
A.R=0.1 B.R=0.2 C.R=0.3 D.R=0.4
A.0.1 B.0.15 C.0.2 D.0.25
A.0.01 B.0.02 C.0.03 D.0.004
A.70° B.60° C.50° D.40°
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