Joe, a hiker, stands at the top of a hill on a trail above the ocean. Joe's friend Dave is just starting out at the trailhead, which is at the beach. Which statement about this scenario is accurate?

The air Joe is breathing is denser than the air at sea level.
The air pressure is higher where Joe is than where Dave is.
If Joe keeps going up, air pressure will continue to decrease.
The air Joe is breathing is denser than the air Dave is breathing.