challenge: Which school districts serve the area of Shell Ridge, California?
  
  A. Acalanes Union High School District and the Pleasanton Unified School District
  B. Walnut Creek Elementary School District and the San Ramon Valley Unified School District
  C. Walnut Creek Elementary School District, Acalanes Union High School District, and the Mount Diablo Unified School District
  D. Mount Diablo Unified School District only
  Answer: 