30.如【圖30】所示電路中,若Vi =10sinωt(伏特),二極體為理想的,則下列敘述何者正確? (A)當ωt = π / 2 時;Vo =15V (B)當ωt= -π / 2 時;Vo = -5V (C)當ωt = π / 6 時;Vo = 0V (D)當ωt= π - π / 6 時;Vo = 0V