______ is the high speed memory used in the computer.

Answer: Option C

Computers use different types of memory. Some are fast, others are slow.
RAM (Random Access Memory) is a type of memory that stores data temporarily while the computer is running. It's fast but loses its data when the computer is turned off.
A Hard Disk is a permanent storage device that holds information even when the computer is off. It's much slower than RAM.
Cache is a very fast type of memory that's even faster than RAM. It stores frequently accessed data to make the computer work quicker.
BIOS (Basic Input/Output System) is a program stored in a special type of memory that starts up the computer. It's not primarily used for general data storage.

Therefore, the answer choices that represent high-speed memory are RAM and Cache. However, Cache is significantly faster than RAM.