**Core Concept**
The microscopic examination of cervical mucus is crucial in assessing the hormonal changes throughout the menstrual cycle. During the post-ovulatory period, the cervical mucus undergoes significant changes due to the surge in progesterone levels, which affect its cellular structure and appearance.

**Why the Correct Answer is Right**
The correct answer is related to the effect of progesterone on cervical mucus. After ovulation, the progesterone levels increase, causing the cervical mucus to become thicker, more viscous, and cellular. This change is due to the presence of **glycogen-rich cells** and **a higher concentration of cholesterol** in the mucus. The glycogen-rich cells are indicative of the post-ovulatory phase, where the mucus becomes less conducive to sperm penetration.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option might refer to the pre-ovulatory phase, where the mucus is more conducive to sperm penetration due to the higher water content and absence of glycogen-rich cells.
* **Option B:** This option might be related to the follicular phase, where the mucus is thinner and more watery, allowing for easier sperm penetration.
* **Option C:** This option might be a distractor, as it does not accurately describe any specific phase of the menstrual cycle.

**Clinical Pearl / High-Yield Fact**
The microscopic examination of cervical mucus is a useful tool in assessing the timing of ovulation and predicting fertility. The presence of glycogen-rich cells in the mucus during the post-ovulatory phase is a key indicator of the progesterone-dominated hormonal environment.

**Correct Answer:** C.