Most traditional human life in deserts is nomadic. It (35) ________ in hot deserts on finding water, and on following infrequent rains to (36) ________ grazing for livestock. In cold deserts, it depends on finding good hunting and fishing grounds, on sheltering from blizzards and winter (37) ________, and on storing enough food for winter. Permanent settlement in both kinds of deserts requires permanent water, food sources and adequate shelter, or the technology and energy sources to (38) ________ it.

Many deserts are flat and featureless, lacking landmarks, or composed of repeating landforms such as sand (39) ________ or the jumbled ice-fields of glaciers. Advanced skills or devices are required to navigate through such landscapes and (40) ________ travelers may die when supplies run (41) ________ after becoming lost. In addition, sandstorms or blizzards may cause disorientation in severely-reduced visibility.

The (42) ________ represented by wild animals in deserts has featured in explorers' accounts but does not cause higher (43) ________ of death than in other environments such as rainforests or savanna woodland, and generally does not affect human distribution. Defense against polar bears may be advisable in some areas of the Arctic. Precautions against snakes and scorpions in choosing (44) ________ at which to camp in some hot deserts should be taken.

It (35) ________ in hot deserts on finding water,