The correct answer is A. Semiconductor memory.
Semiconductor memory is a type of computer memory that uses semiconductor devices such as transistors to store data. It is a volatile type of memory, which means that it loses its contents when the power is turned off. Semiconductor memory is typically used for primary storage, which is the memory that is directly accessible by the CPU.
Magnetic disks, magnetic drums, and magnetic tapes are all types of secondary storage. Secondary storage is a type of computer memory that is used to store data that is not currently being used by the CPU. Secondary storage is typically slower than primary storage, but it has a much larger capacity.
Magnetic disks are a type of secondary storage that uses rotating disks to store data. The disks are coated with a magnetic material, and data is stored on the disks in the form of magnetic patterns. Magnetic disks are a very common type of secondary storage, and they are used in most computers.
Magnetic drums are a type of secondary storage that uses a rotating drum to store data. The drum is coated with a magnetic material, and data is stored on the drum in the form of magnetic patterns. Magnetic drums are less common than magnetic disks, but they are still used in some applications.
Magnetic tapes are a type of secondary storage that uses magnetic tape to store data. The tape is coated with a magnetic material, and data is stored on the tape in the form of magnetic patterns. Magnetic tapes are a very old type of secondary storage, but they are still used in some applications.