A muscle that would only be responsible for the pinky finger would be a small one. In addition, extensor muscles of the hand are located in the posterior compartment, whereas flexors are located anteriorly. Of the following choices, the smallest muscle is the extensor digits minimi, which is also located posteriorly. It aids in abduction of the 5th digit as well.

The correct answer is the radial nerve. This is because the muscle is located in the posterior compartment of the arm, which means we are looking for a nerve that runs deep in the arm. For this reason, the only viable answer choice is the radial nerve.

The abductor digiti minimi is a muscle found in the pinky finger. It is innervated by the deep branch of the ulnar nerve. Its origin is the pisiform and the insertion is the base of the proximal phalanx of the 5th digit on the ulnar side. 

Three muscles attach to the coracoid process in the upper extremity. The pectoralis minor, coracobrachialis, and the short head of biceps brachii all attach to the coracoid process. The pectoralis major does not attach to the coracoid process, but it attaches to the humerus (deltoid also attaches to the humerus).

The musculocutaneous nerve (C5, C6, C7) runs the length of corachobrachialis and brachialis. 

Although all of the muscles listed above extend the wrist, as well as ulnarly or radially deviate the (depending on the muscle and the source being cited), on the extensor carpi radialis longus is able to flex the elbow. The extensor carpi radialis longus attaches more proximally on the humerus than the other wrist extensors, placing it further from the elbow's axis of rotation, which may explain why it can flex the elbow, but the other wrist extensors cannot.

The only muscle listed that receives its primary blood supply from the brachial artery is the biceps (more specifically known as the biceps brachii). 

The other muscles listed receive their blood supply as follows:

Deltoid: Thoracoacromial artery, and anterior and posterior circumflex humeral arteries

Subscapularis: Subscapular artery

Teres major: Subscapular and circumflex scapular arteries

Teres minor: Posterior circumflex humeral artery and circumflex scapular artery

The biceps brachii's main action is flexion of the elbow, and therefore would be the most likely ruptured muscle. Triceps brachii, infraspinatus, and latissimus dorsi are all located posterior on the shoulder complex, and therefore would not perform elbow flexion, or result in a lump on the anterior portion of the upper arm. 

Teres major is not included in the rotator cuff. The rotator cuff muscles insert along the along the head of the humerus, allowing it to move through abduction, internal and external rotation.

The coracobrachialis originates on the coracoid process, and inserts to the medial shaft of the humerus. The cheat in this question is to look at the base word - coracobrachialis.

The rhomboids, which are located medially to the scapula assist with scapular retraction- or the movement of bringing the scapula medially. In addition, the middle trapezius also allows for this movement due to its insertion on the spine, and covering the scapula.