a. The human waste provides food for the mosquito larvae to eat after the eggs hatch.

b. bacteria. decomposition.

c. Gas X is carbon dioxide. It is released by animals during respiration. Thus, mosquitoes may be attracted to this gas to find animals to feed on their blood.

d. Oxygen in the air from the toilet tank was used during decomposition. The air entering the mosquito trap did not have enough oxygen for the mosquitoes to undergo respiration, causing them to die quickly.