When Xiaoping used "Voltammetry" to measure the resistance of small bulbs, he found that the voltmeter pointer did not move after the switch was turned on, and the ammeter had obvious reading. The rea

When Xiaoping used "Voltammetry" to measure the resistance of small bulbs, he found that the voltmeter pointer did not move after the switch was turned on, and the ammeter had obvious reading. The reason may be ( A. If the filament of the light bulb is broken, the ammeter has no indication and the voltmeter has obvious deflection, then option A is wrong;

B, the sliding vane of the sliding rheostat is placed in the position with the largest resistance, so the ammeter has instructions, but there is no obvious deflection, and the voltmeter also has instructions, so B is wrong;

C, because the ammeter is connected in series in the circuit, if the ammeter connection is loose, the ammeter has no indication, so C is wrong;

D, if the voltmeter terminal is in poor contact with the wire, the ammeter has instructions, and the voltmeter has no instructions, which conforms to the meaning of the question, so the D option is correct.

So choose D.