问题
单项选择题
燃气涡轮发动机的进气道一般分为（）两种类型.
A.冲压式进气道和反作用式进气道
B.亚音速进气道和超音速进气道
C.离心式进气道和轴流式进气道
D.单级进气道和多级进气道
答案
参考答案：B
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燃气涡轮发动机的进气道一般分为（）两种类型.
A.冲压式进气道和反作用式进气道
B.亚音速进气道和超音速进气道
C.离心式进气道和轴流式进气道
D.单级进气道和多级进气道
参考答案：B
All living things on the earth need other living things to live with. Nothing lives 1 . Sometimes one living thing kills 2 . Each kind of life eats another kind of life 3 live, and together they form a food chain(食物链). Some food chains are simple, while others are not. But 4 food chains begin with the sun, and all food chains become 5 if one of the links disappears. All life needs sunlight to live on. But only plants can use 6 directly(直接地). They make food from sunlight, water, air and so on. Animals can only use the sun’s energy 7 it has been changed into food by plants. Some animals feed directly on plants. Others eat smaller animals. Meat-eating animals are only 8 plants indirectly. What about human beings? We are members of many food chains. We eat wheat, rice, vegetables, fruits and so on. We also eat meat and drink milk. But 9 often break up the food chains. They kill wild animals. They also make rivers, lakes and seas dirty. When these rivers, lakes and seas are polluted, the fish in them 10 be eaten. If people eat the fish, they will get strange diseases. Each form of life is linked to all the others. Breaking the links puts all life in danger.
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