The correct answer is D. Mass storage.
Primary memory is the computer’s main memory, which is used to store data and instructions that are currently being used by the CPU. It is also known as main storage, primary storage, internal storage, or RAM (random-access memory).
Mass storage is a secondary storage device that is used to store data and programs that are not currently being used by the CPU. It is also known as secondary storage, auxiliary storage, or offline storage.
Main memory is typically much faster than mass storage, but it is also much more expensive. Mass storage is typically much slower than main memory, but it is also much cheaper.
Main memory is volatile, which means that it loses its contents when the power is turned off. Mass storage is non-volatile, which means that it retains its contents even when the power is turned off.
Main memory is typically used to store data and instructions that are currently being used by the CPU. Mass storage is typically used to store data and programs that are not currently being used by the CPU.
In conclusion, the correct answer is D. Mass storage.