According to the circuit diagram, we can see the circuit structure. The lamp L is connected in parallel with ap and then in series with pb, so that the resistance of ap is R 1 and that of pb is R2.

The total resistance of the external circuit is r = r 1rrlr 1+rl+R2,

When the sliding arm P of the sliding rheostat moves from A to B, R 1 becomes larger and R2 becomes smaller. According to mathematical knowledge, the total resistance of the external circuit becomes smaller.

A, according to the ohm's law of closed circuit, the total current will increase, so the indicated value of ammeter will increase, so A is correct.

B. The parallel resistance of lamp L and R 1 is increasing, that is, the voltage across the lamp is increasing, while the terminal voltage of the road is decreasing, so the voltage of R2 is decreasing, that is, the indication of voltmeter is decreasing, so B is correct.

C, the current in the lamp L increases and the total current decreases, so the current in the varistor aP part decreases. So, c is wrong.

D, because the voltage across the lamp increases, the brightness of the lamp L increases. Therefore, d is correct.

So I chose ABD. ..