Answer:
One Vacationing in high Colorado mountains
Explanation:
The difference in air pressure at two locations is felt when the oxygen concentration is different for these two locations.
In general the concentration of oxygen is the same for both the atmosphere above a plain land and above a sea. Therefore, the sister vacationing near sea will not face difficulty in breathing.
While the sister vacationing on mountains will feel air pressure difference due to a decreased oxygen concentration over mountains.
