血液通过肺循环，其变化是（ ）
A．由静脉血变为动脉血
B．由动脉血变为静脉血
C．营养物质减少了，废物减少了
D．营养物质增多了，废物减少了
肺循环是指血液由右心室进入肺动脉，流经肺部的毛细血管网，再由肺静脉流会左心房的循环；在肺循环中，从右心室摄入肺动脉的静脉血，流经肺部毛细血管时，血液中的二氧化碳进入肺泡，肺泡中的氧进入血液，这样，静脉血就变成了动脉血．因此肺循环结束后血液的变化是由静脉血→动脉血．
故选：A
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| "Fit for body, fit for study." is an interesting exercise program of a high school. After 4:20 p.m. all the students of the high school 1 on the playground to run for exercise. Every afternoon from Monday to Friday, one hour before supper the Students at school 2 the playground to run for 40 minutes. The high school started the 3 last winter Why did the school do so? When the winter came, many students were 4 to catch a cold or get sleepy during evening classes. The school was worried about it and then they 5 upwiththe exercise program to make a change. Now most students prefer to 6 an active part in the program and benefit (受益) From it in the high school. It gets my brain (大脑) active and makes me learn more, so I'm ready for 7 classes, said Li Lin in Grade Three. "I'm getting 8 now, so I don't get a cold in winter said Gao Lei in Grade Two. But some students were not 9 inthe program at first However MID months later, the program worked well. Most students didn't get sleepy any more during evening classes-And 10 students got a cold in winter. Actually, the program suited them just fine. Today all the students fall in love with the sport program. They run every-day to keep healthy for their bodies and studies. | ||||
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