Xinjiang patent circuit

If the resistance R is short-circuited, only L is connected in the circuit, and the light bulb becomes bright; So, A is wrong; If R is disconnected, the circuit is disconnected, and the ammeter and voltage representation become smaller, so C is wrong;

If l is short-circuited, the light bulb goes out; If only R is connected in the circuit, the current in the circuit will increase, and the current will increase. At the same time, the voltmeter is short-circuited, so the voltage is reduced; If the lamp L is off, the lamp goes out, the circuit is off, and the current represents zero; At this time, the voltmeter is connected to both ends of the power supply, and the voltage indicates an increase; Then the short circuit and open circuit of the light bulb L meet the meaning of the question, so B is wrong and D is right;

So choose D.