Final answer:
An ammeter is an instrument that measures the current in an electrical circuit, and it must be connected in series with the circuit component to provide an accurate current measurement, making option A. Ammeter the correct answer.
Step-by-step explanation:
An ammeter is a test instrument that measures the amount of current in an electrical circuit. Consequently, the correct answer here is A. Ammeter. To measure the current accurately, the ammeter must be connected in series with the component whose current you wish to measure. This ensures that all of the current flowing through that component also passes through the ammeter, providing an accurate current measurement.
Explanations of concepts such as Ohmmeter, which measures resistance, and Voltmeter, which measures voltage, are also relevant. However, they have distinct functions from an ammeter. An Ohmmeter applies a known voltage across a resistance to measure the current and then uses Ohm's Law to calculate the resistance, while a voltmeter measures the potential difference between two points in an electrical circuit.