## **Core Concept**
The question tests the understanding of hormone classification based on their site of production and mode of action, specifically focusing on orally active hormones. Hormones can be broadly classified into two categories: those that are peptide or protein in nature and are usually administered via injection (due to digestion in the gastrointestinal tract), and those that are steroid hormones, which can be orally active.

## **Why the Correct Answer is Right**
Steroid hormones are derived from cholesterol and are orally active because they can be absorbed from the gastrointestinal tract without being digested. They can diffuse through cell membranes and act on intracellular receptors. **Vitamin D**, which is a secosteroid (a subclass of steroids), is also orally active. Among the given options, if we consider common orally active hormones or substances that act like hormones, **Vitamin D** stands out. Vitamin D is crucial for calcium absorption and bone health, and its deficiency can lead to conditions like rickets in children and osteomalacia in adults.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is blank and cannot be evaluated.
- **Option B:** This option is blank and cannot be evaluated.
- **Option D:** This option is blank and cannot be evaluated.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that steroid hormones (like cortisol, aldosterone, estrogen, progesterone, and testosterone) and Vitamin D are orally active. This is why they can be effectively administered orally in certain medical conditions, unlike peptide hormones (like insulin and growth hormone) which are typically administered via injection.

## **Correct Answer:** .