Mary was born in America and her native language was English

So () I 句型中括号里的内容：如果之前已经提及的是BE动词,则也用BE动词.如：They are studying English and so AM I.如果之前是DO动词,才用DO.如:They all study English and so DO I.这里的意思是MARY出生于美国,（BE born in America）,她的母语是英语（BE English）,而B选项的意思是我也是（这个情况）,it指代the situation.