bush is on time for everything,how can it be

bush is on time for everything,how can it be
Mr.Bush is on time for everything .How____it be that he was late for the opening ceremony?
A.can B.should
选A.我知道how can it be that是怎么可能会.但是为什么不能是should.表示惊讶呢.他一直很准时,这次竟然迟到了.不是很通嘛