Which of the following statements are true?

a. The decrease in the amplitude of an oscillation caused by dissipative forces is called damping.
b. An oscillation that is maintained by a driving force is called forced oscillation.
c. In a mechanical system, the amplitude of an oscillation diminishes with time unless the lost mechanical energy is replaced.
d. The increase in amplitude of an oscillation by a driving force is called forced oscillation.

The true statements are;

a.The decrease in the amplitude of an oscillation caused by dissipative forces is called damping

b.An oscillation that is maintained by a driving force is called forced oscillation

Explanation:

To answer the question, we analyze each of the options as follows;

a.The decrease in the amplitude of an oscillation caused by dissipative forces is called damping.

The above statement is true as damped oscillation is one in which the amplitude is decreased by dissipative forces

b.An oscillation that is maintained by a driving force is called forced oscillation.

When a damped oscillator is allowed to oscillate by itself, it will stop eventually. However when a force is applied to maintain the oscillation the oscillation is then known as a forced oscillation

The above statement is true

c.In a mechanical system, the amplitude of an oscillation diminishes with time unless the lost mechanical energy is replaced.

The above statement is only true in damped oscillation system

d.The increase in amplitude of an oscillation by a driving force is called forced oscillation.

Forced oscillation, as described above, is one the maintains the oscillation of  damped oscillator, therefore, the above statement is not correct.

i would say