单项选择题
A.27 B.28 C.29 D.30
A.0.05d2 B.0.04d2 C.0.315d2 D.0.215d2
A.10~20% B.40~50% C.25~35% D.15~25%
A.7d B.6.7d C.6.8d D.7.33d
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