Question

Mountaineers may suffer from nose bleeding at high altitudes

Answer 1

because at high altitudes they did not get sufficient oxygen for respiration

Answer 2

As the altitude increases the atmospheric pressure decrease. And the air becomes thinner and there will be very less oxygen athigh altitude. So due to which the bloodvessels present inside our their nose bursts and starts bleeding. This is why mountaineers suffer from nose bleeding.
Hope it helps...☺️☺️