A.n>(0.55~0.8)n1 B.n=(0.55~0.8)n1 C.n<(0.55~0.8)n1 D.A+B
A.60n B.6n C.n/6 D.n/60
A.隨機振動頻率 B.固有振動頻率 C.極限轉速 D.臨界轉速