– _________ is he?
– He's fourteen.
A:How big
B:How old
C:How many
D:How much
①用电压表测灯泡两端的电压;
②用电流表测通过灯泡的电流;
③用滑动变阻器改变灯泡的亮度,且滑片P向右移动时灯泡变暗;
④开关控制整个电路.
下图臂章佩用时间转为公元纪年,应是( )