A.主极T1为正,T2为负;门级电压G为正,T2为负B.主极T1为负,T2为正;门级电压G为正,T2为负C.主极T1为正,T2为负;门级电压G为负,T2为正D.主极T1为负,T2为正;门级电压G为负,T2为正