= Solution
The \b[<experimental unit> is a volunteer on a particular afternoon], since that volunteer-session receives a program assignment. There are 36 such <experimental units>; a volunteer is a repeated block, rather than a unit that receives only one program throughout the experiment.
The \b[<observational unit> is the individual completed sketch], equivalently the session's single recorded count of correctly represented features. The separate map features contribute to that <response variable>; they are not independently randomized <replicates>. Nor are repeated sessions on one volunteer independent subjects.
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