(Mary and Tom)math teacher 's 应该加在哪?

(Mary and Tom)math teacher 's 应该加在哪? Tom's and Mary's room后面的room要不要加S,Why? Tom and Mary come from China.错误在哪? Let's go and ask the math teacher啥意思? Tom and Mary's mother 可以表示为（Tom与Mary是兄妹）吗? Tom and Mary’s father 这是Mary的父亲,还是Tom和Mar tom and mary 歌词 She is Mary and Tom’s sister.这句话对吗? -----____school bags are these?-----They are Tom's and Mary' Who's your math teacher? Who s your math teacher? _____school bags are on the desk .A.Mary and Tom's B.Mary's