如图所示电路，已知灯泡的额定电压为3伏，当滑动变阻器滑片P在中点c时电压表示数为2伏，电流表示数为0.2安；当滑片P在a端时，灯泡的实际功率是其额定功率的0.81倍。求：

（1）小灯泡的电阻

（2）电源电压

（3）小灯泡的额定电功率

（4）滑动变阻器的最大阻值

—Look! Jane has ______ tense expression on her face.

—So she does. It seems that ______ news is true.

A．a ; /

B．a ; the

C．the; /

D．the; a