It has gotten dark, and soon the whole family is feeling tired. This is because everyone:

Question

Quizplus · Accepted Answer

The increased darkness signals the body's production of melatonin, a hormone that promotes sleepiness. This is the most likely reason why the whole family is feeling tired as it is getting dark. Option A may be a contributing factor, but without additional information, we cannot assume that everyone had a lot of exercise that day. Option B is unlikely as contagious yawning is not a strong enough force to cause everyone to feel tired at the same time. Option D is also unlikely as serotonin is not typically associated with causing drowsiness.

It Has Gotten Dark, and Soon the Whole Family Is