couple,police,staff等可视作集合名词。。be动词要看具体意义。你说的是一对夫妻,意义上就理解为整体,A couple is watching TV.表复数意像The staff are chatting with each other.表示每个人,主谓一致用复数
A couple is watching TV.用了couple,所以用is
are
A COUPLE IS WATCHING TV