Final answer:
The correct answer is option d. The children would breathe normally while flying on the horse creature, just like birds and other mammals. The lungs allow for efficient respiration and supply the necessary oxygen.
Step-by-step explanation:
When flying on the horse creature, the children would breathe normally. Just like birds, humans and other mammals have lungs, which are specialized organs for gas exchange. Oxygenated air is taken in during inhalation and diffuses across the surface of the lungs into the bloodstream, while carbon dioxide diffuses from the blood into the lungs and is expelled during exhalation.
This process allows for efficient respiration and provides the necessary oxygen for the children to breathe while flying.