**Core Concept**
The question tests the understanding of **cranial nerve anatomy** and **neuro-ophthalmological** conditions, specifically those affecting the **6th cranial nerve (abducens nerve)** and causing **proptosis**.

**Why the Correct Answer is Right**
The correct answer is related to a condition that affects the **cavernous sinus** or **orbital apex**, where the 6th cranial nerve is located, causing **unilateral proptosis** and **bilateral 6th nerve palsy**. This is often seen in conditions like **cavernous sinus thrombosis** or **orbital apex syndrome**.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not typically cause bilateral 6th nerve palsy.
**Option B:** Incorrect as it usually presents with different symptoms.
**Option C:** Incorrect because it is not commonly associated with these specific findings.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **cavernous sinus thrombosis** can cause **bilateral 6th nerve palsy** due to the anatomy of the **cavernous sinus**, where the 6th cranial nerve is located.

**Correct Answer:** D. Cavernous sinus thrombosis.