Have you ever sat on a camel? Well, if you have, then you know how scary it is when the camel rises on its long wobbly(摆动的)legs. The rocking motion of a camel is a bit like a being tossed around in heaving seas. Small wonder then that the camel is often called the ship of the desert. Actually, the name owes its origins to the fact that camels were brought from the desert, to serve as beasts of burden in other countries.

We in India are only familiar with one species of camel, known as the Dromedary camel. This animal is singlehumped, has long legs and is found in the deserts of Asia and Africa. Another specie(the twohumped shortedlegged Bactrian camel)is found in parts of China and Central Asia.
Recently, scientists discovered what they think is a new species of wild camel that lives in a remote part of China. These mammals look very similar to the Bactrian camel but they have a unique feature—they survive by drinking salty water.
Strangely enough, scientists knew about the existence of the animal, but had no idea of their unique identity(特性). As a result, researchers now admit that these animals are not Bactrian camels as initially(最初)thought, but a new species. The only visible physical difference is that the saltwater drinking species has its humps further apart than the Bactrian camel.
Camels are most common in the African and Asian deserts, but fossil evidence shows that camels originated in North America about 45 million years ago. So how did they manage to come into Africa? Well, million of years ago, North America and Asia were connected by a land mass—the presentday Bering Strait.
Scientists think that the camels migrated into South America and across to Asia, disappearing almost entirely from the land of its origin. However, many researchers say that the South American llama(骆驼)is a direct descendant of the camel.
The camel is called“the ship of the desert”because________.

A．when you are on a camel, you feel like being on a ship at sea

B．its long legs swung when it is traveling in the desert

C．camels came from the desert and are used in other countries

D．camels can travel in the desert of many days without eating

What's the difference between the Dromedary camel and the Bactrian camel?

A．The Dromedary camel has two humps.

B．The Bactrian camel has long legs.

C．The Dromedary camel is only found in Asia.

D．The Dromedary camel has only one hump.

What scientists don't know about the new species is________.

A．their existence in China

B．their ability to survive on salty water

C．their similarity to the Bactrian water

D．how they survive in the remote part of China

How can people tell the new species from the the Bactrian camel?

A．By looking at the length of their legs.

B．By counting the number of humps.

C．By looking at the distance of the two humps.

D．By examining the kind of the two humps.

From the passage we can infer that________.

A．Very few camels exist in North America at present

B．Camels warm across the Bering Strait to Asia

C．Camels first originated from the African deserts

D．Camels are the most endangered animals in the world