How much sleep do we need? We are all different. Some people need only three hours of sleep a night. 1 need ten hours of sleep a night. After age fifty, the average (平均) sleep time goes 2 to 6.5 hours a night. Most of people have a night when they can't sleep. About one in three Americans has a problem with 3 Many of these people 4 fall sleep. This is not 5_ problem. Many famous people 6 could not fall asleep. Some of these people had their own ways to make them sleep. Benjamin Franklin, the famous statesman and inventor had four 7 . He 8 from one to the other to fall asleep. King Lois XIV of France has 413 beds and hoped _ 9_ asleep in one of them Mark Twain, the famous American writer, had a different way. He lay 10 _ his side across the end of the bed!
Colour helps you see things.But man and some monkeys and apes(猿) are the only mammals(哺乳动物) that can see colour.1 any other mammals,such as the dog,the world 2 a black-white photo.Dogs hunt mainly by listening and smelling.
Like 3 animals,dogs see best when things move.The animals they hunt seem to know this.A rabbit or deer will freeze when they find that they are being hunted.Then the dog 4 see it at all
Birds can see colour.They need to,because when they fly,they need to find places to land.Colour helps them know 5 the place is and what it is like so that they are able to catch flying things in the air or to 6 something they think safe.
Some birds see things even 7 than man.The birds that eat bugs(虫子) can see them from far away.And even a very young bird can see a house 8 the sky.So good eyes and being able to see colours help birds 9 food and also help them find out 10 there are other animals that are dangerous to them.