Passage Summary: Researchers found that dolphins can sense electric fields, but this ability disappears if you cover specific tiny organs on their noses.

Reasoning: Dolphins avoid electric fields under normal conditions, but they stop reacting to those fields when the small organs on their snouts are covered with plastic.

Analysis: This stimulus describes a controlled experiment using the 'method of difference.' By covering the vibrissal crypts and observing that the dolphin's reaction disappears, the researchers have isolated the variable responsible for the behavior. You should look for an answer that concludes these crypts are the sensory organs used for electroreception. In 'Must be True' or 'Most Strongly Supported' questions involving experiments, the correct answer almost always points to the causal link established by the change in conditions.