John and Mary were at home yesterday.
即用and,at 因为后面的谓语动词是were,显然主语是复数,即and连接的两个人,如果用with,表示伴随,主语只能是John,是单数.另外,在家是at home.
这道题出现在我的求助里,不然有这么多答了,我不会故意和他们撞题的.