问题
单项选择题 B型题
梨形心（）。
A.二尖瓣关闭不全
B.二尖瓣狭窄
C.主动脉瓣狭窄
D.主动脉瓣关闭不全
E.三尖瓣关闭不全
答案
参考答案：B
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梨形心（）。
A.二尖瓣关闭不全
B.二尖瓣狭窄
C.主动脉瓣狭窄
D.主动脉瓣关闭不全
E.三尖瓣关闭不全
参考答案：B
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| Thousands of years ago, people did not know 1 to make a fire. When it was very 2 at night, they could not sleep well. Sometimes lightning hit (打, 击) a 3 and started a fire. At first people were both surprised and 4 to see the fire. They were afraid to go up. Later a few 5 men took some of this fire and made a fire near their homes. They used the fire to keep them warm and to cook food. When they had a fire, they did not let it 6 burning. If it stopped, they could not start it again. Maybe they had to 7 for a long time, sometimes for 8 . Later they 9 how to make a fire with pieces of wood. Now we have matches, we can put them in our pockets and make a fire when we want to make it. But we have to be 10 with fire. | ||||
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