**Core Concept**
The tumor described in the question is a type of testicular germ cell tumor, which is a heterogeneous group of neoplasms that arise from the germ cells of the testis. These tumors can exhibit a wide range of histological patterns, making their diagnosis challenging.

**Why the Correct Answer is Right**
The microscopic features described in the question, including lobules containing large cells with watery cytoplasm, primitive glomeruli, syncytiotrophoblast, and undifferentiated cells with focal glandular differentiation, are characteristic of a choriocarcinoma. Choriocarcinoma is a highly malignant type of germ cell tumor that often produces beta-human chorionic gonadotropin (β-hCG). The presence of syncytiotrophoblast, which is responsible for β-hCG production, is a key feature of this tumor.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because embryonal carcinoma is a type of germ cell tumor that typically exhibits a more primitive, undifferentiated appearance, often with a "rosette" or "pseudoglandular" pattern. While it can exhibit a range of differentiation, the specific features described in the question are not typical of embryonal carcinoma.

**Option B:** This option is incorrect because yolk sac tumor (also known as endodermal sinus tumor) typically exhibits a distinctive "Schiller-Duval" body, which is a glomerulus-like structure with a central blood vessel surrounded by tumor cells. While the question mentions structures resembling primitive glomeruli, this is not a definitive feature of yolk sac tumor.

**Option C:** This option is incorrect because teratoma is a type of germ cell tumor that exhibits a wide range of differentiation, including tissue types from all three germ layers (ectoderm, endoderm, and mesoderm). While teratoma can exhibit a range of histological patterns, the specific features described in the question are not typical of this tumor.

**Clinical Pearl / High-Yield Fact**
Choriocarcinoma is a highly malignant type of germ cell tumor that can produce β-hCG, which can lead to elevated serum levels of this hormone. This can be an important diagnostic clue in patients with testicular cancer.

**Correct Answer:** C. Choriocarcinoma.