The correct answer is: A. ammeter.
A moving-coil permanent-magnet instrument can be used as an ammeter by using
a low resistance shunt. A shunt is a conductor with a low resistance that is connected in parallel with the moving-coil instrument. The shunt allows a larger current to flow through the instrument, which in turn causes the needle to deflect more. This allows the instrument to measure larger currents.A voltmeter is used to measure voltage. It does this by connecting the voltmeter in parallel with the component whose voltage is being measured. The voltmeter has a high resistance, which prevents current from flowing through the component and causing it to change its voltage.
A flux-meter is used to measure magnetic flux. It does this by connecting the flux-meter in series with the component whose magnetic flux is being measured. The flux-meter has a low resistance, which allows current to flow through the component and cause it to produce a magnetic field.
A ballistic galvanometer is used to measure the amount of charge that flows through it. It does this by measuring the deflection of the needle when a known amount of charge is passed through it.
I hope this helps!