A.瞬時值的絕對值成正比 B.積分成反比 C.瞬時值的絕對值成反比 D.積分成正比
A.0°≤≤60° B.90°≤≤180° C.0°≤≤120° D.30°≤≤60°
A.50% B.75% C.80% D.85%