Question Options:
a. caffeine
b. insomnia
c. narcolepsy
d. sugar
Answer: Xi is feeling this way because of CAFFEINE.
Explanation: Caffeine is an alkaloid, C8H10N4O2, found naturally in tea and coffee plants which acts as a mild stimulant on the central nervous system.
Usually people take caffeine to make them "ready for the day". It's stimulation effect is believed to give energy and keep one active.
As a result of Xi consuming several cups is cola that contains caffeine, his nervous system has been stimulated and thereby kept active causing him to be unable to sleep.