**Core Concept**
Human chorionic gonadotropin (hCG) is a glycoprotein hormone produced during pregnancy, playing a crucial role in maintaining the corpus luteum, thereby supporting embryonic development. It is secreted by the placenta, specifically by the cytotrophoblast and syncytiotrophoblast cells.

**Why the Correct Answer is Right**
hCG has structural and functional similarities to luteinizing hormone (LH), allowing it to stimulate the corpus luteum and maintain progesterone production. This is essential for the establishment and maintenance of pregnancy. The placenta produces hCG from the 10th day of gestation, and its levels peak at around 10-12 weeks of pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because hCG is not secreted by the ovaries. While the ovaries do produce and secrete various hormones, hCG is not among them.

**Option B:** Incorrect because hCG is not secreted by the pituitary gland. Although the pituitary gland is responsible for secreting LH, hCG is a separate hormone produced by the placenta.

**Option C:** Incorrect because hCG is not secreted by the adrenal glands. The adrenal glands produce various hormones, including cortisol and aldosterone, but hCG is not among them.

**Option D:** Incorrect because hCG is not secreted by the pancreas. The pancreas produces hormones like insulin and glucagon, but hCG is not produced by this organ.

**Clinical Pearl / High-Yield Fact**
hCG is used as a marker in pregnancy tests and is also used in the management of certain types of cancer, such as choriocarcinoma and germ cell tumors.

**Correct Answer:** C. The placenta.