Passage Summary: Two guards have strict rules: they can only leave their posts to chase an escaping prisoner or when their relief arrives. On a specific night, one guard followed the rules perfectly, but the other one did not.

Reasoning: The rules state that guards must leave only if pursuing an escapee or if their replacement arrives; on May 11, Chelas broke these rules while Stelma followed them.

Analysis: In a 'Must be False' question, we are looking for a statement that flatly contradicts the established rules and facts. Since we are told Stelma followed the rules, any scenario where Stelma left the station without an escapee or a replacement would be impossible. Conversely, because Chelas violated the rules, he must have either left when he wasn't supposed to or failed to leave when he was required to. Look for an answer choice that describes Stelma acting in a way that would constitute a violation or Chelas acting in a way that would be perfectly compliant.