Passage Summary: Microwaved milk loses more enzymes than stove-heated milk even when they reach the same temperature, so the author thinks the microwaves are the problem, not the heat.

Conclusion: The destruction of the lysozyme enzyme is caused by the microwaves themselves, not by the heat they generate.

Reasoning: Milk heated to 50 degrees by a microwave loses more enzymes than milk heated to 50 degrees by a conventional source.

Analysis: The argument assumes that '50 degrees' means the same thing in both heating methods. To weaken this, look for an answer that suggests the microwave method actually involves higher temperatures than the conventional method, despite the final reading. If microwaves create localized 'hot spots' that exceed 50 degrees while the thermometer only measures the average, then heat could still be the culprit. We want to find an alternative explanation for why the microwaved milk lost more enzymes.