**Core Concept:**
The glenohumeral joint is a ball-and-socket joint in the upper limb, connecting the scapula (shoulder blade) and humerus (upper arm bone). It has a large range of motion but lacks stability without the support of surrounding muscles, ligaments, and nerves. In this question, we discuss the mechanisms preventing downward dislocation of the glenohumeral joint during lifting a suitcase.

**Why the Correct Answer is Right:**
The correct answer, "B. Levator scapulae," is the right choice because it is a muscle that originates from the upper cervical spine and inserts onto the scapular blade. Its function is to elevate the scapula, which contributes to maintaining the stability of the glenohumeral joint during activities like lifting heavy objects or carrying out overhead tasks.

**Why Each Wrong Option is Incorrect:**

A. "Deltoid muscle" is incorrect because its main function is to flex, abduct, and rotate the humerus, but not specifically to prevent downward dislocation of the glenohumeral joint during lifting.

C. "Rhomboid muscles" are also incorrect because their primary role is to retract the scapula and stabilize the scapulothoracic joint, not preventing downward dislocation of the glenohumeral joint.

D. "Pectoralis major muscle" is not the correct answer as it primarily functions to adduct and elevate the humerus, not to stabilize the glenohumeral joint during lifting tasks.

**Clinical Pearl:**
Understanding the role of different muscles in maintaining shoulder joint stability is crucial for preventing shoulder injuries while performing overhead activities. In clinical practice, knowledge of these muscles helps in devising an appropriate rehabilitation program or addressing shoulder complaints accurately.