某患者舒张期二尖瓣口心动图所示,提示()
A.二尖瓣狭窄
B.二尖瓣关闭不全
C.二尖瓣脱垂
D.正常声像图
E.二尖瓣赘生物
参考答案:A
Statistics showed that approximately 40 percent of all marriages in the United States end in divorce. ()
A.show
B.have shown
C.shows
D.are shown
如图所示,中子内有一个电荷量为+23e的上夸克和两个电荷量为-13e的下夸克,3个夸克都分布在半径为 r 的同一圆周上,则3个夸克在其圆心处产生的电场强度为( )
A.ker2
B.ke3r2
C.ke9r2
D.2ke3r2