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    Plants are very important. This is because plants can make food from air, water and sunlight. Animals and man cannot make food from air, water and sunlight. Animals can get their food by eating plants and other animals. Man gets his food by eating plants and animals, too. So animals and man need plants to live. This is why there are so many plants around us.
    There are two kinds of plants: flowering plants and non-flowering(无花) plants. Almost all the trees around us are flowers and fruit. Non-flowering plants don't grow flowers. You can't see many non-flowering plants around you.
    If you look carefully at the plants around you, you'll find that there are many kinds of plants. Some plants are very big and some very small. Most of them are green. We can live on the earth because of the plants around us.

在学完相关知识后，某同学利用废旧电线设计制作了如图所示三种血管关系的模型，模型中，①和③是稍粗一点的电线，②是细铜丝．下列描述正确的是（　　）