**Core Concept**
The sensitivity of nerve fibers to hypoxia refers to their ability to detect and respond to oxygen deprivation. Among the types of sensory neurons—A, B, and C fibers—**B fibers** are unmyelinated, slow-conducting nociceptors that detect pain and temperature, and are particularly sensitive to hypoxic conditions due to their high metabolic demand and role in detecting tissue ischemia.

**Why the Correct Answer is Right**
B fibers are the most sensitive to hypoxia because they are primarily involved in detecting ischemic pain and tissue injury. These fibers have a high metabolic rate and are directly affected by reduced oxygen supply, leading to early activation during hypoxia. Unlike A fibers (which carry fast pain and touch) and C fibers (which carry slow pain and temperature), B fibers are specifically tuned to respond to metabolic stress such as hypoxia. Their sensitivity makes them key in early warning of tissue hypoxia.

**Why Each Wrong Option is Incorrect**
Option A: A fibers are myelinated and conduct rapidly, but they are less sensitive to hypoxia due to their role in sharp, acute sensations rather than metabolic stress.
Option C: C fibers are slow-conducting and respond to chronic pain and temperature, but they are less sensitive to hypoxia compared to B fibers.
Option D: This is incorrect because B fibers are not equally sensitive; they are specifically more sensitive due to their metabolic vulnerability.

**Clinical Pearl / High-Yield Fact**
In ischemic events like myocardial infarction or stroke, B fiber activation leads to early pain and discomfort—this is a key clinical sign of tissue hypoxia. Always remember: **B fibers = hypoxia sensitivity**.

✓ Correct Answer: B. B