Answer:b) Microsleeps are occurring due to the sleep deprivation, and he is asleep for brief periods of time.
Step-by-step explanation:
Micro-sleep refers to a period of dozing off or sleeping temporary for a fraction of a second to 30 seconds which causes a person to be unable to respond to certain sensory situation and for that moment it like they are unconscious; they can not see or feel anything in those seconds during which micro-sleep hit them.
So for a second a person is awake and another they are not awake and there is a shift between these two states.
A person drifts off slowly and has their eyelids shutting down slowly until they shut completely or slightly and they head goes down to their chest as if they are nodding .
It usually happens when a person has not had enough sleep like Sid in the above text which is making it hard for him to see the S on the screen.