If the alarm rings, then the guard checks the gate. If the guard checks the gate, then the logbook is signed. It is known that the guard checks the gate. Which of the following must be true?
Correct answer B. The logbook is signed.
Explanation
Since the guard checks the gate, the second rule shows that the logbook is signed. Nothing can be said about whether the alarm rings, because a true result does not prove its condition.
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