**Core Concept**
The brachial plexus is a complex network of nerves that originate from the spinal cord in the neck and innervate the muscles of the arm. Each nerve root contributes to the formation of the plexus, and injury to a specific nerve root can result in distinct patterns of neurological deficits.

**Why the Correct Answer is Right**
The C5 nerve root contributes to the suprascapular nerve, which innervates the supraspinatus and infraspinatus muscles. These muscles are responsible for stabilizing the scapula and facilitating movements such as abduction and rotation of the arm. When the suprascapular nerve is injured, the scapula may "wing" due to the weakness of these muscles, resulting in an abnormal appearance and limited range of motion. This is a classic sign of a C5 brachial plexus injury.

**Why Each Wrong Option is Incorrect**
**Option A:** Loss of abduction of the arm is not a direct consequence of a C5 brachial plexus injury, as the deltoid muscle, which is responsible for abduction, is primarily innervated by the axillary nerve (C5-C6).
**Option B:** Loss of abduction of arm is a vague and incomplete statement, as abduction is a complex movement involving multiple muscles and nerves. A C5 brachial plexus injury would not necessarily result in a complete loss of abduction.
**Option C:** Loss of shrugging is more closely associated with a C6 brachial plexus injury, as the trapezius muscle, which is responsible for shrugging, is primarily innervated by the spinal accessory nerve (C3-C4) and the suprascapular nerve (C5).

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the pattern of neurological deficits resulting from a brachial plexus injury can provide critical clues about the level and extent of the injury. A thorough understanding of the anatomy and innervation of the brachial plexus is crucial for accurate diagnosis and management.

**✓ Correct Answer: D. Winging of scapula**