The nurse did not think that the symptoms ___________ an emergency room visit.

The correct choice, "warranted," accurately fits the context of the sentence. "Warranted" means justified or necessitated, indicating that the nurse did not believe the symptoms justified the need for an emergency room visit. In this scenario, it conveys the idea that the nurse assessed the symptoms and found them lacking in urgency.

The other options do not convey the same meaning or fit grammatically within the sentence structure. "Desired" suggests a want or preference, which is not appropriate in this context. "Guaranteed" implies a certainty that does not relate to justifying actions based on symptoms. Lastly, "should have" introduces a different construction that does not seamlessly fit with the rest of the sentence, as it does not clearly relate to the idea of justification for an emergency visit. Thus, "warranted" is the most suitable choice, reflecting the nurse's professional assessment of the situation.