**Core Concept**
The corpus luteum of the ovary is a temporary endocrine structure that produces estrogen and progesterone in the luteal phase of the menstrual cycle. Its continued function is crucial for maintaining pregnancy through the secretion of human chorionic gonadotropin (hCG), which mimics luteinizing hormone (LH) and supports the corpus luteum.

**Why the Correct Answer is Right**
The corpus luteum of pregnancy is maintained by the secretion of human chorionic gonadotropin (hCG) from the placenta. hCG is a hormone produced by the trophoblast cells of the placenta, which stimulates the corpus luteum to continue producing estrogen and progesterone. This hormone replacement maintains the corpus luteum of pregnancy, ensuring that progesterone levels remain high and supporting the implantation of the embryo in the uterine lining. The hCG produced by the placenta is responsible for maintaining the corpus luteum until the placenta takes over the production of progesterone in the second trimester.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the corpus luteum is not maintained by the secretion of follicle-stimulating hormone (FSH) from the pituitary gland. While FSH is essential for follicular development, it does not play a role in maintaining the corpus luteum of pregnancy.

**Option B:** This option is incorrect because the corpus luteum is not maintained by the secretion of estrogen from the placenta. While estrogen is an essential hormone produced by the placenta, it does not maintain the corpus luteum of pregnancy.

**Option D:** This option is incorrect because the corpus luteum is not maintained by the secretion of progesterone from the placenta. While progesterone is an essential hormone produced by the placenta, it does not maintain the corpus luteum of pregnancy.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that human chorionic gonadotropin (hCG) is produced by the trophoblast cells of the placenta and is responsible for maintaining the corpus luteum of pregnancy. hCG levels are often used as a marker of pregnancy and can be detected in urine and blood tests.

**Correct Answer: C. The placenta. The corpus luteum of the ovary is maintained by the secretion of human chorionic gonadotropin from the placenta.**