About 750 years ago, a man named Marco Polo went to China. He started in Europe and traveled more than 5, 000 miles. He crossed some large deserts. The journey took almost three years. There were no planes or trains then. So how did Polo make the trip? He rode a camel.
Like horses, camels can work as pack animals. They can carry many pounds of cargo (货物), such as food and supplies. That is very helpful for a long trip. They act as "ships of the desert".
Camels do well in the desert. They can go for several days without water. They can survive a long time without food, too.
There are two kinds of camels. One kind has one hump. The other has two. These humps store fat. If needed, the fat turns into water.
Camels have other special ways to deal with desert life. They have a thick coat. This keeps them warm at night and cool in the day. They have long eyelashes and an extra eyelid. These help protect their eyes. Camels also have thick lips. They can eat all kinds of plants, even thorny ones.
They are not picky about food. That is good because few plants grow in deserts. They also have very large feet. These help camels walk on sand. Camels can run on sand, too. They can go about 25 miles per hour. That's about as fast as a racing bicycle.
Camels have carried people and things for thousands of years. Today they play other roles in the modern world, too.
① They have a thick coat. ② They only eat thorny plants.
③ They have short eyelashes. ④ They have an extra eyelid.
