--- Why is Linlin practicing speaking English?
--- abroad for further study.
A:Go
B:Gone
C:To go
D:Goes
二面角a-AB-b的平面角是锐角,点C∈a且点C不在棱AB上,D是C在平面b 上的射影,E是棱AB上满足∠CEB为锐角的任意一点,则( )
①上腔静脉②左心房③右心房④左心室⑤右心室⑥肺动脉⑦肺静脉
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