**Core Concept**
Endodermal sinus tumors (ESTs), also known as yolk sac tumors, are a type of germ cell tumor that arise from the yolk sac of the embryo. They are characterized by the presence of specific histological features, including Schiller-Duval bodies, which are a hallmark of this tumor type.

**Why the Correct Answer is Right**
Schiller-Duval bodies are pathognomonic structures composed of a central blood vessel surrounded by embryonic tissue within a space lined by tumor cells. The presence of these structures is a diagnostic criterion for endodermal sinus tumors. These tumors are malignant in nature, producing high levels of alpha-fetoprotein (AFP), but not human chorionic gonadotropin (HCG). They are most commonly seen in the ovaries of young females, particularly in the first two decades of life.

**Why Each Wrong Option is Incorrect**
**Option A:** Schiller-Duval bodies are indeed seen in endodermal sinus tumors, making this option correct, so it's not a distractor. However, for the sake of explanation, this option is accurate and should be acknowledged as the correct answer.

**Option B:** Endodermal sinus tumors are not benign; they are malignant in nature, which makes this option incorrect.

**Option C:** These tumors do not typically produce elevated HCG levels; instead, they are associated with high levels of AFP, making this option incorrect.

**Option D:** While endodermal sinus tumors are indeed seen in young individuals, this option does not provide any specific information about the tumor itself and is therefore a distractor. However, it is not incorrect, as these tumors are more common in young females.

**Clinical Pearl / High-Yield Fact**
Remember the "S-D-AFP" acronym to associate Schiller-Duval bodies with endodermal sinus tumors and the production of alpha-fetoprotein.

**Correct Answer:** A. Schiller duval bodies seen