**Core Concept**
The lining of the fallopian tube is composed of a specialized epithelial layer that plays a crucial role in fertilization and early embryonic development. This epithelial layer is characterized by ciliated cells, secretory cells, and peg cells, which work in concert to facilitate the process of fertilization and implantation.

**Why the Correct Answer is Right**
The correct answer is **D. Pseudostratified columnar epithelium**. This type of epithelium is composed of tall, columnar cells that appear to be layered due to their varying heights. In the context of the fallopian tube, this epithelial lining is responsible for secreting substances that help to nourish the fertilized egg and facilitate its movement through the tube. The cilia on these cells also play a crucial role in propelling the egg towards the uterus.

**Why Each Wrong Option is Incorrect**
**Option A:** Squamous epithelium is incorrect because it is typically found in areas that are exposed to the external environment, such as the skin and oral cavity. It is not characteristic of the fallopian tube lining.

**Option B:** Simple columnar epithelium is incorrect because it lacks the stratified appearance of pseudostratified columnar epithelium. While simple columnar epithelium is found in some areas of the female reproductive tract, it is not the characteristic lining of the fallopian tube.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the epithelial lining of the fallopian tube plays a critical role in fertilization and early embryonic development. Damage to this lining, such as that caused by pelvic inflammatory disease, can lead to infertility and other reproductive complications.

**Correct Answer:** D. Pseudostratified columnar epithelium