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Do you know Pleasure of Farmhouse(农家乐)? It's a new way for holidays in China. Now, more and more people are interested in it, especially young people. Every weekend, thousand of people drive to the countryside. The farmers invite them to their farms even homes. Many people help the farmers work on the farms, such as fishing, watering the crops or picking apples. If you come to the farm, you will fall in love with the country life at once. Here you can listen to the birds, enjoy the beautiful view of countryside, breathe the fresh air and watch the crops grow. You can even taste the fresh produce, such as tomatoes and strawberries.

Pleasure of Farmhouse brings a good chance to enjoy the life of countryside, especially for people living in the cities. It can make them relax.

      One farmer said, “Welcome children to our farms. We will show you where your food comes from.”

人体血液静置一段时间后会出现分层现象。上层透明的液体是____ ，下层红色不透明的液体主要是____ ，两层交界处有一层白色的物质，这主要是____ 和____ 。

观察下面的结构示意图，在①②两处应分别填入（   ）