单项选择题

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