The correct answer is C. ALU.
The ALU (Arithmetic Logic Unit) is the part of the computer that performs arithmetic and logical operations. It is the part of the computer that does the actual calculations. The ALU is made up of logic gates, which are electronic circuits that can perform simple operations such as AND, OR, and NOT. The ALU can also perform more complex operations such as addition, subtraction, multiplication, and division.
The disk unit is the part of the computer that stores data. It is made up of one or more disks that are coated with a magnetic material. Data is stored on the disks in the form of magnetic patterns. The disk unit can read and write data to the disks.
The control unit is the part of the computer that controls the execution of instructions. It is responsible for fetching instructions from memory, decoding them, and executing them. The control unit also communicates with the other parts of the computer to coordinate their activities.
The modem is a device that converts digital signals to analog signals and vice versa. It is used to connect computers to the internet. The modem is not used for calculating or comparing.
Therefore, the correct answer is C. ALU.