These people, getting ready to travel across the desert to look for a new place to live in, must water their camels．The camel driver tries to get each camel to drink as much water as possible because the little water that these people take along will be needed by themselves．
A very big camel can hold more water than some cars can hold gasoline (汽油)． That's why the camel can go for many days without having to drink． It's a good thing that camel can do this, because it may have to in the great，dry desert．
Nomads (游牧民) never keep their homes in one place very long．They're always moving．That's what Nomads are—people who wander around instead of living in one place．
Every time the Arab Nomads set out across the hot, sandy desert，it is a new adventure．They must find food for the animals, or the animals will die．

The Nomads wander from one place to another because（）.