An alternating current is one which changes its:
A) Direction
B) Magnitude
C) Magnitude and direction both
D) None

Hint: An alternating current is a current which performs a specific cycle of time period by changing its magnitude and direction. It contains frequency, varying amplitude and direction. An alternating current is generated from an AC generator which uses split signs which change the direction of AC after a fixed interval of time.

Complete step by step answer:
An alternating current is a current whose magnitude and direction both changes after a fixed interval of time. There are two types of current namely Direct current and Alternating current. Unlike AC, DC does not change its direction and magnitude after a cycle. An alternating current follows a sine wave graph and contains an expression i.e. $y = a\sin \omega t$ where y= wave of AC, a=amplitude and $\omega$ =angular frequency of AC. AC has varying amplitude so its root mean square value is calculated to get the preferred fixed value. In India the value of AC for residential is 220V and its frequency is 50Hz. This means AC changes its direction after 1/50 secs. All the appliances work on DC current. In all the appliances there is a device called a rectifier which converts AC to DC. But if we provide DC supply directly to the appliances then they will not work because of the rectifier.

Note: For an AC it is necessary to change its direction and magnitude. That’s why it is called alternating current. This property of varying magnitude is because of its source of generation. AC is generated from an AC generator. Whereas DC has opposite properties.