**Core Concept**
In an infertile woman with proliferative endometrial changes, the preferred hormone is one that promotes ovulation, endometrial differentiation, and corpus luteum formation. This involves a delicate balance of estrogen and progesterone to prepare the endometrium for a potential pregnancy.

**Why the Correct Answer is Right**
Estrogen promotes endometrial proliferation, but progesterone is essential for endometrial differentiation and preparation for implantation. In a woman with proliferative endometrial changes, the addition of progesterone will induce secretory changes, which are necessary for a receptive endometrium. This is particularly important in the context of infertility, where the goal is to create an optimal environment for implantation.

**Why Each Wrong Option is Incorrect**
* **Option A:** While estrogen is essential for endometrial proliferation, it is not sufficient on its own to prepare the endometrium for implantation. Estrogen alone would perpetuate proliferative changes.
* **Option B:** Progesterone alone would induce secretory changes, but without a preceding estrogen-induced proliferation, the endometrium may not be receptive to implantation.
* **Option D:** This option is incomplete and does not provide a specific hormone.

**Clinical Pearl / High-Yield Fact**
In the context of infertility, it's essential to achieve a balance between estrogen-induced proliferation and progesterone-induced differentiation to create a receptive endometrium for implantation.

**Correct Answer:** C. Progesterone.