It's the International Show-and-Tell Competition and Arnold and DA are representing Ms. Frizzle's class. Arnold brings a webbed hoop, left behind by his great-aunt Arizona Joan, the famous archaeologist, but he has no idea what it is! Using clues from the hoop and Joan's journal, the kids make educated guesses about its uses. To test their hypotheses, Ms. Frizzle turns the bus into a ""Supposatron,"" a magical device designed to evaluate guesses. Can the kids solve the puzzle before Arnold and DA take the stage? With Alex Trebek as the ""Sportscaster.""
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