Mountaineers carry oxygen cylinders with them because (a) there is no oxygen on high mountains (b) there is deficiency of oxygen on mountains at high altitude (c) oxygen is used for cooking oxygen keeps them warm at low temperature.

• Solution:

(b): there is deficiency of oxygen on mountains at high altitude

As higher we go, the atmosphere gets thinner and the supply of oxygen is reduced. This makes difficulty in breathing on hill stations and mountains. Therefore, while climbing high mountains, mountaineers carry oxygen cylinders with them.