**Core Concept**
The posterior cord is a part of the brachial plexus, a complex network of nerves that arise from the spinal cord and supply the upper limb. It is formed by the union of nerve fibers from the posterior divisions of the middle and inferior trunks.

**Why the Correct Answer is Right**
The posterior cord is responsible for supplying the muscles of the posterior arm, including the triceps brachii, and the skin of the posterior arm and forearm. It contains the radial nerve, which is a major branch that supplies the muscles of the posterior arm and forearm, and the axillary nerve, which supplies the deltoid and teres minor muscles. The posterior cord also gives rise to the upper subscapular and lower subscapular nerves, which supply the subscapularis and teres major muscles.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct nerves or muscles supplied by the posterior cord.
**Option B:** This option is incorrect because it does not accurately describe the nerves or muscles supplied by the posterior cord.
**Option C:** This option is incorrect because it does not specify the correct nerves or muscles supplied by the posterior cord.

**Clinical Pearl / High-Yield Fact**
The posterior cord is often remembered using the mnemonic "RAT" for Radial, Axillary, and Thoracodorsal (T) nerves, which are the major branches that arise from it.

**Correct Answer: A. Posterior cord supplies the triceps brachii, skin of the posterior arm and forearm, and the muscles of the posterior arm and forearm via the radial nerve.**