**Core Concept**
The question requires the identification of a precursor molecule that serves as a common substrate for the synthesis of both gonadal and adrenocortical hormones. This involves understanding the biosynthesis pathways of steroid hormones, particularly the role of cholesterol and its derivatives.

**Why the Correct Answer is Right**
The correct answer is cholesterol, which is a precursor molecule for the synthesis of both gonadal and adrenocortical hormones. Cholesterol is converted into pregnenolone by the enzyme cholesterol desmolase (also known as P450scc), which is a key enzyme in the biosynthesis of steroid hormones. Pregnenolone is then further converted into various steroid hormones, including progesterone, cortisol, aldosterone, and sex hormones such as testosterone and estrogen. The conversion of cholesterol to pregnenolone is a rate-limiting step in the biosynthesis of steroid hormones.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it is not a precursor molecule for steroid hormone synthesis.
**Option B:** This option is incorrect as it is not a precursor molecule for steroid hormone synthesis.
**Option D:** This option is incorrect as it is not a precursor molecule for steroid hormone synthesis.

**Clinical Pearl / High-Yield Fact**
Cholesterol is the primary precursor molecule for the synthesis of steroid hormones, including gonadal and adrenocortical hormones. The conversion of cholesterol to pregnenolone is a rate-limiting step in the biosynthesis of steroid hormones, and defects in this step can lead to various disorders, including congenital adrenal hyperplasia.

**Correct Answer:** C. Cholesterol.