A multimeter is a versatile electronic device that is used to measure various electrical quantities. It combines multiple measurement functions into a single instrument, making it a valuable tool for electricians, technicians, and hobbyists. The correct answer to the question is option 'D', which states that a multimeter can measure current, resistance, and voltage. Let's explore each of these measurements in detail:

1. Measuring Current:
- A multimeter can be used to measure electric current flowing through a circuit.
- It is accomplished by connecting the multimeter in series with the circuit, allowing the current to pass through the instrument.
- The multimeter's current measurement function is typically denoted by the symbol "A" (amperes) on the selection dial.
- It is important to select the appropriate range on the multimeter to avoid damage or inaccurate readings.

2. Measuring Resistance:
- Another capability of a multimeter is measuring electrical resistance.
- Resistance is the opposition to the flow of electric current in a circuit.
- By using the resistance measurement function of a multimeter, you can determine the resistance of a resistor, a circuit component, or the continuity of a wire.
- The resistance measurement function is usually denoted by the symbol "Ω" (ohms) on the selection dial.
- It is important to disconnect the component or circuit being measured from any power source before measuring resistance.

3. Measuring Voltage:
- Multimeters are commonly used to measure voltage, which is the potential difference between two points in an electrical circuit.
- By connecting the multimeter in parallel across a circuit or component, you can measure the voltage accurately.
- The voltage measurement function on a multimeter is typically denoted by the symbol "V" (volts) on the selection dial.
- It is crucial to select the appropriate voltage range on the multimeter to avoid overloading the instrument and obtaining incorrect readings.

In summary, a multimeter is a versatile tool that can measure current, resistance, and voltage. It allows individuals to troubleshoot electrical circuits, test components, and ensure proper functioning of electrical systems. The ability to perform these measurements makes a multimeter an essential device in the field of electronics.