Which of the following represents Alternating Current?

Alternating Current, commonly abbreviated as AC, is the correct representation of the current that periodically reverses direction. In an AC circuit, the voltage and current fluctuate sinusoidally over time, which is a fundamental characteristic of how this type of electricity is generated and used in various applications, including residential and commercial power systems.

This is distinct from Direct Current (DC), which flows consistently in one direction, and would therefore not be the correct answer for AC. The other options, marked as MC or SC, do not represent any recognized terms for electrical current types in conventional usage. AC is widely used due to its efficiency in transmitting power over long distances and its ability to easily transform voltages through transformers, making it a crucial concept to understand in electrical systems and installations.