**Core Concept**
Frostbite rewarming involves carefully warming the affected area to reverse tissue damage and minimize complications. The ideal temperature for rewarming is crucial to prevent further tissue damage.

**Why the Correct Answer is Right**
The correct temperature for rewarming frostbite is between 40°C to 42°C (104°F to 108°F). This temperature range is warm enough to facilitate blood flow and tissue repair without causing additional damage. Research has shown that rewarming at temperatures above 42°C can lead to additional tissue damage due to the denaturation of proteins. In contrast, rewarming at temperatures below 40°C may not effectively restore blood flow and promote tissue repair.

**Why Each Wrong Option is Incorrect**
**Option A:** 37°C (98.6°F) - This temperature is too close to normal body temperature and may not provide sufficient warmth to promote blood flow and tissue repair.
**Option B:** 50°C (122°F) - This temperature is too high and can cause additional tissue damage due to protein denaturation.
**Option C:** 20°C (68°F) - This temperature is too low and may not effectively restore blood flow and promote tissue repair.

**Clinical Pearl / High-Yield Fact**
When rewarming frostbite, it's essential to avoid using hot water or direct heat sources, as this can cause further tissue damage. Instead, use lukewarm water or a warm compress to gradually increase the temperature.

**Correct Answer:** C. 40°C to 42°C.