## **Core Concept**
The question tests knowledge of reproductive endocrinology, specifically the role of Follicle-Stimulating Hormone (FSH) in the reproductive system. FSH is a key hormone involved in the regulation of the reproductive cycle, acting on specific cells in the ovaries and testes. Understanding the target cells of FSH is crucial for comprehending reproductive physiology and pathology.

## **Why the Correct Answer is Right**
FSH primarily acts on the **granulosa cells** of the ovarian follicles in females and on the **Sertoli cells** in males. In females, FSH stimulates the growth of ovarian follicles, which produce estrogen. In males, FSH, in conjunction with testosterone, supports spermatogenesis by acting on Sertoli cells, which nurture the developing sperm cells. The correct answer, therefore, targets these cells.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately represent the primary target cells for FSH action.
- **Option B:** This is incorrect as it does not specify the correct cell type for FSH action.
- **Option C:** This option might seem plausible but does not accurately represent the primary target for FSH.
- **Option D:** This option is incorrect because, like the others, it does not accurately identify the granulosa cells (in females) or Sertoli cells (in males) as the target for FSH.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that FSH levels can be used to assess ovarian reserve in women. Elevated FSH levels can indicate diminished ovarian reserve or premature ovarian failure. In men, abnormal FSH levels can indicate issues with spermatogenesis.

## **Correct Answer:** . Granulosa cells.