Both Mary and Jane understands English.为何不是understand?

Both Mary and Jane understands English.为何不是understand? Both mary and Jane like music.(改同意句) Jane and Mary ( ) 21 years old Dear Aunt Mary,Jane and I. Mary's and Jane's /Mary and Jane's ( ) fathers work in the same company. 单选 要翻译! I invited Mary and Jane to dinner,but__of them came. A.none B.either C.both D.neither Both Tom and Mary (like) (play) football. Jane and Mary 可以看成是一个整体吗? Mary and Jane are twins.But they are( ). Mary is eight and Jane is nine.改为同义句 Jane and Mary are sisters.T--------- parents are teachers The book shelf over there is ------填所有格,是Mary's and jane还是Mary and jane's 1.Mary and Jane are in the same grade.(改写,意思不变)Mary and Jane are（）in（）grades. Mary and Jane are in the same grade改写意思不变Mary and Jane are （ ）in（ ）grades Both Tony and Mary want to be tennis ______(player) Both Mary ang I think our English teacher is the most popular at school.A.so does Jane B.so jane does C .so jane is D.so is jane 这句话对吗?Tom and Mary both have won prizes.为什么不把both和have Mike and Mary are both nine years old.同义句：Mike ____ ____ ____ Mary.