想选A,不过又觉得后面应该用has been on.求真解.
问题描述：
想选A,不过又觉得后面应该用has been on.求真解.
Could you tell me when.
It...since the president came.
A.the ceremony will begin,has begun.B.the ceremony began,has been on
答
A,看标志词since,要用完成体
B属于完成进行体