计算题：已知如图所示的R、L串联电路中，UR=110V，U=220V，试求L上的电压有效值UL。
参考答案：
电压有效值为190.5V。
It was only when I reread his poem recently _____ to appreciate its beauty.
A．that I began
B．did I begin
C．I began
D．until I began
心绞痛发作的典型部位为 （）
A.胸骨体下段
B.胸骨体中段或上段胸骨后
C.心前区
D.心尖区
E.剑突下
