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!