Most commonly nerve fibre affected by pressure is:

**Core Concept**
The question tests the understanding of nerve fiber physiology and the effects of external pressure on different types of nerve fibers. **Pressure** can damage nerve fibers by disrupting axonal transport and causing demyelination.

**Why the Correct Answer is Right**
Although the specific correct answer is not provided, it is known that **large myelinated nerve fibers** are more susceptible to pressure damage. This is because these fibers have a larger diameter and are more easily compressed, leading to disruption of axonal transport and nerve conduction.

**Why Each Wrong Option is Incorrect**
**Option A:** If this option were a small unmyelinated fiber, it would be incorrect because these fibers are less susceptible to pressure damage due to their smaller size.
**Option B:** Similarly, if this were another type of fiber, it would be incorrect for the same reason as Option A.
**Option C:** Without knowing the specifics, if this option represented a type of nerve fiber less commonly affected by pressure, it would be incorrect.
**Option D:** This option would be incorrect if it did not represent the most commonly affected nerve fiber type.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that nerve fiber damage due to pressure can lead to various clinical manifestations, including numbness, tingling, and weakness.

**Correct Answer:** Not provided in the query.