单项选择题
A.退扭 B.半退扭 C.不退扭 D.退扭、不退扭均可
A.2.3d1 B.2.25d1 C.2.35d1 D.2.4d1
A.6d B.6.15d C.6.44d D.5.7d
A.72% B.78% C.84% D.90%
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