—You watched the fashion show last night, didn't you?

—Yes, ________I missed the beginning. [ ]

A. so  

B. but

C. and

D. yet

如图4所示，理想变压器的原线圈输入电压不变的交变电流，副线圈上接有定值电阻R和两个相同的灯泡和L2，其余导线电阻不计．当S闭合时(      )

A．M、N两端的电压减小

B．电阻R两端的电压增大

C．通过原线圈的电流减小

D．通过灯泡的电流减小