１、划线部分是“事或物”，特殊疑问词用what　

eg: This is a bag. ---What is this?

We often play football on Sundays . ---What do you often do on Sundays ?

２、划线部分是“人”，特殊疑问词用who

eg:She is my sister. ---Who is she ?

３、划线部分是“地点”，特殊疑问词用where

eg:The apple is on the desk.---Where is the apple ?