**Core Concept**
The question tests the understanding of vitamin deficiencies and their association with specific diets, particularly in carnivores. **Vitamin C deficiency** is a key concept here, as it is related to the dietary intake of certain animals.

**Why the Correct Answer is Right**
Vitamin C, also known as **ascorbic acid**, is essential for various bodily functions, including collagen synthesis and iron absorption. Carnivores, unlike herbivores, can synthesize their own vitamin C from glucose in the liver, thanks to the enzyme **L-gulonolactone oxidase**. However, some animals, like humans, lack this enzyme and require dietary vitamin C.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the question is about a vitamin deficiency exclusive to carnivores, which does not apply to a general vitamin deficiency.
**Option B:** Similarly, this option does not specify a vitamin deficiency unique to carnivores.
**Option D:** This option is also incorrect as it does not relate to the specific dietary needs of carnivores.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **vitamin C deficiency** leads to **scurvy**, characterized by fatigue, malaise, and connective tissue defects.

**Correct Answer:** D. Vitamin C