题目内容：

阅读下面短文，根据短文内容完成句子。

Many ways to sleep

How do you sleep? Most people sleep on their backs or sides. Do animals sleep the same way? Actually, the ways they sleep are much more different — they can lie down, sit or stand while they sleep.

Swiss scientists did a study on 250 different mammals (哺乳动物). They found that the animals’ sleeping postures (姿势) had something to do with their size and weight.

Small animals with short legs sleep on their stomachs. Their body shape is perfect for this posture. They also like to put their legs under their bodies. Rabbits and cats sleep this way.

But larger animals sleep differently. They lie on their sides. That’s because this is more comfortable for their longer legs. Cows and hippos (河马) often sleep like this.

However, there are exceptions. Small animals such as mice sometimes sit down to take a short nap. Some large animals such as horses, zebras and giraffes sleep standing up. This way, they can immediately run away if they are in danger.

Did you know? Albatrosses are large seabirds. They can sleep while flying. They can even do that while flying at a speed (速度) of about 40 km an hour.

1.The ways animals sleep are much more________.

2.Animals’ sleeping postures have something to do with their________.

3.Rabbits and cats like to put their legs________ when they sleep.

4.Giraffes sleep standing up in order to run away________if they are in danger.

5.To our surprise albatrosses can sleep while________at a high speed.