The correct answer is A. A register.
A register is a high-speed storage location that can be used to store data or instructions. It is a small amount of fast memory that is built into the CPU. Registers are used to store data that is being processed by the CPU, as well as instructions that are being executed.
A bus is a data pathway that connects different parts of the computer. It is used to transfer data between the CPU, memory, and other devices.
A databus is a type of bus that is used to transfer data between the CPU and memory. It is a set of parallel lines that carry data bits.
Therefore, the correct answer is A. A register.