单项选择题
A.10~20% B.40~50% C.25~35% D.15~25%
A.7d B.6.7d C.6.8d D.7.33d
A.80~85° B.70~75° C.75~80° D.85~90°
A.2 B.2.5 C.3.0 D.3.5
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