The correct answer is B. Magnetic core.
A magnetic core is a small ring of magnetic material, typically ferrite, used in magnetic core memory. Magnetic core memory was the most common type of computer memory from the 1950s to the 1970s. It was replaced by semiconductor memory, which is much faster and more dense.
Magnetic tape is a long, thin strip of plastic coated with a magnetic material. It is used for storing data, such as computer programs and files. Magnetic tape is a sequential access storage device, which means that data can only be accessed in the order in which it is stored.
Magnetic disk is a flat, circular platter coated with a magnetic material. It is used for storing data, such as computer programs and files. Magnetic disk is a random access storage device, which means that data can be accessed in any order.
Optical mark reader is a device that reads data from specially marked paper. It is used to scan test papers, ballots, and other documents. Optical mark readers are typically used in large-scale applications, such as standardized testing.
None of the above is a type of internal storage.