Text stimulus (table): A district sampling table titled Schools and Planned Probability Sample. Columns: School, Enrollment, Planned Random Sample. Rows: North High, 1800, 180; East High, 1200, 120; Central High, 900, 90; South High, 600, 60. Note: Goal is district-wide estimate. No method names. A district wants results it can defend as representing all high school students across schools of different sizes. Which plan is strongest?