单项选择题
A.1/2~1圈 B.1~2圈 C.2~3圈 D.3~4圈
A.400mm B.500mm C.800mm D.1000mm
A.10% B.20% C.30% D.40%
A.互相平行 B.成45° C.成60° D.互相垂直
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