9. The mountaineers carry oxygen with them because:
(a) At an altitude of more than 5 km there is no air.
(b) The amount of air available to a person is less than that available on the ground.
(c) The temperature of air is higher than that on the ground.
(d) The pressure of air is higher than that on the ground.
The mountaineers carry oxygen with them because the amount of oxygen availability to a person is less than that available on the ground. (b)
As we move higher in altitude, the density of the atmosphere lessens.