单项选择题
A.5s B.10s C.15s D.20s
A.1/4~2/3 B.1/2~2/3 C.1/3~2/5 D.1/3~3/5
A.15° B.30° C.45° D.60°
A.5%~10% B.10%~15% C.15%~25% D.25%~30%
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