Answer:
E. Where
Step-by-step explanation:
The sentence gives us information about when the school band is holding a car wash (this Saturday), who is doing the main action (the school band), what is it doing (holding a car wash), and the purpose or why the school band is holding a car wash (to raise money for its trip to the Rose Bowl). It does not give us information, however, about the place where this activity is taking place.