The correct answer is B. Control unit.
The control unit is the part of a computer that is responsible for coordinating the various operations of the computer. It does this by sending out timing signals to the other parts of the computer, telling them when to perform their tasks.
The arithmetic-logic unit (ALU) is responsible for performing arithmetic and logical operations. The memory unit is responsible for storing data and instructions. The input/output unit is responsible for communicating with the outside world.
None of the other options are responsible for coordinating various operations using timing signals.