Do you know what the world's tallest animals are? How do they sleep and drink? You may think they have （困难）while sleeping but actually giraffes don't often stop to （休息）. As they are so tall that they can grow up to 18 feet and need the shortest sleep of all mammals, with an average of half an hour a day. When they fall （睡着）, they hardly lie down and sleep for minutes at a time, because it's hard for them to get up again from the （地面）and it's dangerous in the wild. But the giraffe in the zoo sleeps around 4-6 hours a day, （主要地）at night. Drinking water is also hard for the giraffe because of the long （脖子）. To drink, they must spread the legs in an uncomfortable way and if so they will be easily caught by other animals. So, they get most of water from plants to （保护）themselves.
