Aeroplanes having wings fly at low altitudes while jet planes fly at high altitudes . Way ?

Why do aeroplanes having wings fly at low altitudes?

What is the cause of altitude sickness at high altitudes?

Persons living at high altitude will have

"Sky aooears dark to passengers flying at very high altitudes" why ?

Weight of a person can be zero when 1. he is falling freely 2. he is orbiting in a satellite 3. he is in aeroplane flying at a high altitude. 4. he is having ride in a gas filled balloon.

Weight of a person can be zero when 1. he is falling freely 2. he is orbiting in a satellite 3. he is in aeroplane flying at a high altitude. 4. he is having ride in a gas filled balloon.

Statement -1 : Aeroplanes always fly at low altitudes. Statement -2 : Ac cording to Newton's third law of motion, for every action there is an equal and opposite reaction.

The sky appears dark to passengers flying at a very high altitude. Why?