The revival of an extinguished CR (conditioned response) is called:

Generalization

Extinction

Spontaneous recovery

Acquisition

Spontaneous recovery

Explanation:

An individual takes a sweat inducing injection in a dark room. This act of sweating is an Unconditional Response to the Unconditioned Stimuli which is the Injection.

After some time, whenever the individual is in a dark room, he begins to sweat. This is now a Conditioned Response (Sweating) to a Conditioned Stimuli (The Dark room).

If after some time, this conditional response lessons and goes away, it is referred to as Extinction.

However, after a period of absence, if the Conditioned Response returns, it is referred to as Spontaneous Recovery.