**Core Concept**
Granulosa cell tumors are a type of sex cord-stromal tumor that arise from the granulosa cells of the ovarian stroma. These tumors are known for their potential to produce estrogen, leading to various clinical manifestations.

**Why the Correct Answer is Right**
The correct marker for granulosa cell tumors is inhibin. Inhibin is a protein complex produced by granulosa cells in the ovaries and Sertoli cells in the testes. It plays a crucial role in regulating the production of follicle-stimulating hormone (FSH) by the pituitary gland. Inhibin is specifically elevated in granulosa cell tumors, making it a valuable marker for diagnosing these tumors.

**Why Each Wrong Option is Incorrect**
**Option A:** Not mentioned - There are no established markers associated with granulosa cell tumors other than inhibin.
**Option B:** CA-125 is a tumor marker for various conditions, including ovarian cancer, but it is not specific for granulosa cell tumors.
**Option C:** AFP (Alpha-fetoprotein) is a marker for yolk sac tumors, not granulosa cell tumors.
**Option D:** LDH (Lactate dehydrogenase) is a nonspecific enzyme marker that can be elevated in various conditions, including some types of cancer, but it is not specific for granulosa cell tumors.

**Clinical Pearl / High-Yield Fact**
Inhibin is a useful marker for diagnosing granulosa cell tumors, especially in cases where imaging studies are inconclusive. A high inhibin level can help differentiate granulosa cell tumors from other types of ovarian tumors.

**Correct Answer:** A. Inhibin.