**Core Concept**
Dysgerminoma is a type of germ cell tumor that arises in the ovaries, characterized by its rapid growth and potential for metastasis. Tumor markers are substances produced by cancer cells that can be detected in the blood or urine, helping diagnose and monitor the disease.

**Why the Correct Answer is Right**
Beta-hCG (human chorionic gonadotropin) is a tumor marker that can be elevated in germ cell tumors, including dysgerminoma. This is because dysgerminoma cells can produce beta-hCG, which is a hormone normally produced during pregnancy. Elevated levels of beta-hCG can indicate the presence of a germ cell tumor, particularly in cases where imaging studies are inconclusive.

**Why Each Wrong Option is Incorrect**
**Option A:** CA-125 is a tumor marker commonly associated with epithelial ovarian cancers, not germ cell tumors like dysgerminoma. Elevated CA-125 levels are not specific for dysgerminoma.
**Option B:** AFP (alpha-fetoprotein) is a tumor marker that can be elevated in certain types of germ cell tumors, such as yolk sac tumors, but not typically in dysgerminoma.
**Option C:** LDH (lactate dehydrogenase) is a nonspecific enzyme that can be elevated in various conditions, including malignancies, but is not a specific tumor marker for dysgerminoma.

**Clinical Pearl / High-Yield Fact**
In cases of suspected germ cell tumors, including dysgerminoma, it's essential to measure beta-hCG and AFP levels, as elevated levels can guide further diagnostic and therapeutic decisions.

**Correct Answer:** B. Beta-hCG.