Why does a plastic bottle that is sealed at a high altitude change its shape when it is taken to a low altitude?

At high altitude, the air pressure outside the sealed bottle is relatively low. When the bottle is taken to a lower altitude, the denser air has more gas molecules striking its outside, increasing the external pressure. The trapped air inside cannot quickly equalize the pressure, so the bottle changes shape. The correct choice is A, that more gas molecules strike the outside as altitude decreases.

AI-written and checked against the verified answer.