**Core Concept**
The nasopharynx is a critical anatomical region that forms part of the upper airway, extending from the base of the skull to the upper surface of the soft palate. It is a complex area with various structures, including muscles, fossae, and bony landmarks.

**Why the Correct Answer is Right**
The correct answer involves understanding the anatomical relationships and landmarks of the nasopharynx. The nasopharynx is bounded by the sphenoid bone and the basilar process of the occipital bone superiorly, the soft palate inferiorly, and the torus tubarius anteriorly. The fossa of Rosenmüller is a shallow depression located on the lateral wall of the nasopharynx, corresponding to the opening of the Eustachian tube. Passavant's ridge, formed by the palatopharyngeus muscle, is a muscular structure that helps to close the nasopharyngeal isthmus during swallowing. The lower border of the nasopharynx corresponds to the upper border of the soft palate.

**Why Each Wrong Option is Incorrect**
* **Option A:** Passavant's muscle is actually formed by the palatopharyngeus muscle, not the stylopharyngeus muscle.
* **Option B:** The fossa of Rosenmüller corresponds to the opening of the Eustachian tube, not the internal carotid artery (ICA).
* **Option C:** The lower border of the nasopharynx actually corresponds to the upper border of the soft palate, not the upper faucial pillar.

**Clinical Pearl / High-Yield Fact**
The nasopharynx is a critical area for the development of certain head and neck cancers, such as nasopharyngeal carcinoma. It is essential for clinicians to be aware of the anatomical landmarks and relationships in this region to accurately diagnose and manage these conditions.

**Correct Answer: D. Lower border lies at the level of soft palate.**