**Question:** The root value of axillary nerve is

A. C5
B. C6
C. C7
D. C8, T1

**Core Concept:**
The axillary nerve is a peripheral nerve that arises from the brachial plexus, which is formed by the union of the cervical roots C5, C6, C7, C8, and T1. The axillary nerve plays a crucial role in the innervation of various structures in the upper limb.

**Why the Correct Answer is Right:**
The axillary nerve is formed by the union of cervical roots C5, C6, C7, C8, and T1. Out of these, root values C5, C6, and C7 contribute to the formation of the axillary nerve. Therefore, the correct answer is C5, C6, and C7 combined.

**Why Each Wrong Option is Incorrect:**
A. C5: While C5 contributes to the formation of the axillary nerve, it is not the only root involved.
B. C8: C8 also contributes to the formation of the axillary nerve, but T1 is the last contributing root.
C. T1: T1 is the last root that contributes to the formation of the axillary nerve.

**Clinical Pearl / High-Yield Fact:**
Understanding the origin and structure of peripheral nerves like the axillary nerve is essential for understanding their functions and clinical implications. In cases of nerve injuries or disorders, knowledge of these roots can guide the diagnosis and treatment plan.

In summary, the correct answer is C5, C6, and C7 combined, as these roots contribute to the formation of the axillary nerve. Each wrong option is incorrect due to the specific contributions of the cervical roots to the axillary nerve formation.