单项选择题
A.60° B.75° C.86° D.90°
A.1:1 B.1:3 C.1:2 D.1:4
A.10~20KN B.20~60KN C.70~80KN D.80~100KN
A.1/2圈 B.1/4圈 C.1/3圈 D.1圈
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