题干
The students stopped talking__________ the teacher came into the classroom.
A：when
B：until
C：and
D：so
答案(点此获取答案解析）
A
The students stopped talking__________ the teacher came into the classroom.
A：when
B：until
C：and
D：so
的坐标为（1，4）、（5，4）、（1、
），则
外接圆的圆心坐标是
