B.
有两个会议.
如果用have,要用人.
We are going to have two meetings in our school next month．
举办会议呀,比赛呀.都是如此.
There is going to be a football match tomorrow．
We are going to have a football match tomorrow．
懂了吗?
两个会议.当然应该选复数了.一个会议就用is了.
There is going to be a meeting．．．．
There are going to be two meetings．．．