如图是心脏结构示意图．根据图回答问题．
（1）写出④名称：④______，其内的血液是______血．
（2）图中⑤的名称是______．
（3）正常情况下，心室收缩时，⑥流入______（写图中序号）
心脏的结构为：①主动脉；②肺动脉；③肺静脉；④左心房；⑤房室瓣；⑥左心室；⑦右心室
（1）由肺循环的途径：右心室→肺动脉→肺部毛细血管→肺静脉→左心房．在肺循环中，血液流经肺部毛细血管网时，与肺泡进行气体交换，血液中的二氧化碳进入肺泡，肺泡内的氧进入血液．这样，静脉血就变成了动脉血．所以，左心房内流动的是动脉血．
（2）房室瓣是心房和心室之间的瓣膜，其作用是防止血液倒流，使血液只能从心房流向心室．
（3）体循环的路线为：左心室→主动脉→全身各级动脉→全身各处毛细血管→全身各级静脉→上、下腔静脉→右心房．所以，左心室收缩时，血液流入主动脉．
故答案为：（1）左心房；动脉血
（2）房室瓣
（3）①
请仔细阅读下面的一篇短文，按信息表中的项目要求填写信息。 Dear Tom, Thank you for your postcard. I show it to some of my friends at school. Three other people in my class have friends in other countries, too. Now I want to tell you something about my family. My father and mother are teachers. I have a brother and a sister. My sister works in a middle school and my brother is studying at a university（ 大学 ）. I am a middle school student. I am 12 years old. I am tall and a little fat. I have short hair. I like reading and playing the guitar. I always play it on Saturdays and Sundays. I like my English teacher very much. Because she is kind to us and her class is fun. Could you give a few photos of yours? I want to know what you look like. Yours, Huang Lei
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