Catatonia
a. is a state of immobility and unresponsiveness that lasts for long periods of time.
b. means giving personal meaning to completely random events.
c. refers to false, unusual, and sometimes magical beliefs that are not part of an individual's culture.
d. refers to sensory experiences that occur in the absence of real stimuli.

refers to sensory experiences that occur in the absence of real stimuli

Explanation: Technically, Catatonia can be defined as a severe psychiatric condition, often associated with schizophrenia, that is characterized by a tendency to remain in a rigid state of stupor for long periods which give way to short periods of extreme agitation.

The short periods of extreme agitation can be said to be sensory experiences that occur in the absence of real stimuli.