that girl looks like her mother.(同义)

题目

that girl looks like her mother.(同义)
that girl and her mother ____ ____ ____ .
再问个I will be back.为什么要加be

答案

1.That girl looks like her mother.
= That girl and her mother (look the same).
2.I will be back.为什么要加be
back是副词,不是动词,所以不能放在will后面一起做谓语.
所以必须加上be动词原形be,一起和back形成系表结构.