**Core Concept**
The question is testing the knowledge of the muscles of the arm, specifically their functions and actions. The muscle in question is responsible for flexion and supination of the forearm.

**Why the Correct Answer is Right**
The correct muscle is the Biceps Brachii, which has two heads: the long head and the short head. The Biceps Brachii muscle originates from the supraglenoid tubercle of the scapula and the coracoid process, and inserts into the radial tuberosity. It is a two-joint muscle, acting on both the shoulder and elbow joints. The Biceps Brachii is responsible for flexion of the elbow and supination of the forearm. The supinator action is provided by the biceps brachii's deep head and the supinator muscle's action on the radius.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the Brachialis muscle primarily acts on the elbow joint, producing flexion, but does not have a significant supinator action.
* **Option B:** This option is incorrect because the Brachioradialis muscle primarily acts on the forearm, producing flexion, but does not have a significant supinator action.
* **Option C:** This option is incorrect because the Pronator Teres muscle primarily acts on the forearm, producing pronation, but does not have a significant supinator action.

**Clinical Pearl / High-Yield Fact**
The Biceps Brachii muscle is also responsible for the bicipital aponeurosis, which helps to stabilize the shoulder joint. This is an important consideration for surgeons performing shoulder surgeries.

**Correct Answer:** B. Biceps Brachii