**Core Concept**
Mummification is a natural process of preservation where the body undergoes desiccation, preventing decay and decomposition. This process involves the removal of moisture from the body tissues, which can occur due to various environmental factors.

**Why the Correct Answer is Right**
Mummification is indeed characterized by the preservation of external features, as the skin remains intact and relatively unchanged. High atmospheric temperatures can accelerate the mummification process by increasing evaporation and dehydration. Additionally, a dry air environment is conducive to mummification, as it allows for the rapid removal of moisture from the body tissues. This process is often seen in arid regions where the climate is hot and dry.

**Why Each Wrong Option is Incorrect**
**Option A:** "External features are preserved" is partially correct, but the question is asking about the conditions necessary for mummification, not just the outcome. This option doesn't address the environmental factors involved.
**Option B:** "High atmospheric temperature is needed for" is partially correct, but mummification can also occur in cold temperatures if the air is dry. Temperature alone is not sufficient for mummification.
**Option C:** "Occurs in dry air" is partially correct, but mummification can also occur in hot temperatures without necessarily being in dry air.

**Clinical Pearl / High-Yield Fact**
It's essential to note that mummification can occur in various environmental conditions, not just hot and dry climates. The process of mummification is complex and influenced by multiple factors, including temperature, humidity, and air movement.

**Correct Answer Line**
✓ Correct Answer: D. All of the above