**Core Concept**
The Dawn phenomenon, also known as the diurnal cortisol surge, is a physiological increase in blood glucose levels that occurs in the early morning, typically between 2-8 am. This phenomenon is characterized by an increase in glucose production and insulin resistance, leading to hyperglycemia.

**Why the Correct Answer is Right**
The Dawn phenomenon is a result of the natural circadian rhythm of cortisol and growth hormone release, which stimulates gluconeogenesis and glycogenolysis in the liver. As cortisol levels rise in the early morning, it promotes the breakdown of glycogen to glucose and the production of new glucose through gluconeogenesis. This increase in glucose production, combined with insulin resistance, leads to an increase in blood glucose levels.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while cortisol does play a role in the Dawn phenomenon, it is not the sole feature of this phenomenon.
**Option B:** Incorrect because insulin resistance is a consequence of the Dawn phenomenon, not a feature of it.
**Option C:** Incorrect because while growth hormone does contribute to the increase in glucose production, it is not the primary feature of the Dawn phenomenon.

**Clinical Pearl / High-Yield Fact**
The Dawn phenomenon is a common cause of morning hyperglycemia in patients with diabetes, and it can be managed with medications that reduce cortisol levels or increase insulin sensitivity.

**Correct Answer: C. Increase in glucose production and insulin resistance in the early morning due to natural circadian rhythm of cortisol and growth hormone release.**