**Core Concept**
Progesterone is a **steroid hormone** crucial for the menstrual cycle and pregnancy. It is produced by the **corpus luteum** in the ovaries after ovulation. The production of progesterone is essential for preparing the uterus for a potential pregnancy.

**Why the Correct Answer is Right**
The correct answer is related to the site of **progesterone production**, which involves the **ovary**, specifically the **corpus luteum**. This structure forms from the ruptured **follicle** after **ovulation** and starts producing **progesterone** to support early pregnancy by maintaining the **endometrium**.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not the primary site of progesterone production in the context of the menstrual cycle and early pregnancy.
**Option B:** Incorrect as it is not directly related to the production of progesterone.
**Option C:** Incorrect because, although the placenta does produce progesterone during pregnancy, the question context suggests the initial production before placental takeover.
**Option D:** Incorrect as it is not the correct site of progesterone production.

**Clinical Pearl / High-Yield Fact**
Remember, **progesterone** levels are crucial for the **luteal phase** of the menstrual cycle, supporting implantation of the embryo and early pregnancy.

**Correct Answer:** D. Corpus luteum of the ovary, placenta, but primarily corpus luteum initially.