— Mary works really hard and she does well in her tests.

— Well, ________.

A．you reap what you sow

B．that’s her feet of clay

C．she is the apple of our eyes

D．that’s her cup of tea

有两个标有“6V-2W”和“12V-8W”字样的灯泡，若将它们串联接人电路，电路两端允许的最大电压是______V．