[单选题](单选题)女,45岁,劳累性呼吸困难、心悸1年余。体检:心尖区S1亢进及二尖瓣开放拍击声,并有舒 张中晚期隆隆样递增型杂音,P2亢进,超声心动图显示二尖瓣呈城墙样改变,前后叶同向运动,开放受限,瓣口面积为0.8cm2。诊断应考虑为 A. 二尖瓣脱垂 B. 二尖瓣狭窄伴关闭不全 C. 二尖瓣狭窄 D. 二尖瓣关闭不全 E. 左房黏液瘤
A. around Sagittarius A were found quite unexpectedly B. are common phenomena surrounding enormous black holes C. only flow away from the centers of galaxies D. are the true source of intense energy 参考答案:B 答案解析:根据文章第五段第二和第三句话“This expanding gas is similar in temperature,density,and com position to the jets of