The correct answer is C. damping.
A damping device is a mechanical device that reduces the amplitude of oscillations in a system. It does this by absorbing energy from the system, which can be done in a number of ways. One common way is to use friction, which converts mechanical energy into heat. Another way is to use viscous damping, which converts mechanical energy into fluid flow energy.
Damping is important in a number of applications, such as controlling the vibration of machines and preventing the oscillation of pendulums. It is also used in shock absorbers, which help to reduce the impact of bumps in the road when driving a car.
The other options are not correct. A deflecting device is a device that changes the direction of a moving object. A controlling device is a device that regulates the operation of a machine or system. Any of the above is not a complete answer, as it does not specify which of the options is correct.