如果他从来不帮我，我为什么要帮他？

___Why ___should I help him if he never helps me?

如果她想要，她为什么不能买辆新车？

___Why ___shouldn't she get a new car if she wants one?

既然我能看电影，为什么还要读这本书？

___Why ___should I read the book when I can watch the movie?