I will go to see my grandma before I ____ (leave) Garden City.这是动_英语解答

I will go to see my grandma before I ____ (leave) Garden City.
这是动词适当形式填空.请从语法角度解释,

人气：323 ℃　时间：2019-08-20 12:20:47

解答

I will go to see my grandma before I _leaving___ (leave) Garden City.
这种情况用动名词