با توجه به متن به 5 سوال بعدی پاسخ دهید. They aren't the most beautiful animals in the world. But in the hot lands of North Africa and in the Middle East they are certainly one of the most useful. But how much do you know about camels? Camels normally live for about 40 years but they usually stop working when they are about 25 years. Camels don't normally like running- it's too hot- but when they need to, they can run at 20 kilometers an hour. The dromedary, or Arabian camel, has one hump. The Bactrian, or Asian camel, has longer hair and has got two humps. There are about 14 million camels in the world, and most of them are dromedaries. An adult camel is about 2.1 meters tall and weigh about 500 kilograms. Camels can walk for more than 600 kilometers without drinking water. They only need to drink water every six or eight days. But when there is water, they can drink up to 90 litres. Camels, according to the passage, .............. .