心尖部触及舒张期震颤，提示
A．二尖瓣关闭不全B．二尖瓣狭窄C．室间隔缺损D．动脉导管未闭E．主动脉瓣关闭不全
参考答案：B
The teacher didn't begin the class _____ all the students _____. [ ]
A. until, stopped to talk
B. before, stopped to talk
C. when, stopped talking
D. until, stopped talking
土地确权是一项（），其结果具有法定性和权威性。
A.法律行为
B.行政行为
C.政府行为
D.集体行为
