A function of the trapezius muscle is to:

The trapezius muscle plays a critical role in the movement and stabilization of the shoulder region. Its primary functions include moving and stabilizing the scapula (shoulder blades), which is essential for proper arm movement. The trapezius helps with actions such as shrugging the shoulders, rotating the scapula, and extending the neck.

The correct response highlights the importance of the trapezius in stabilizing the shoulder blades as it allows for a wide range of arm movements, including lifting and swinging. When the trapezius is engaged and functioning correctly, it supports the arms' motions and ensures that they can move freely and effectively.

In contrast, flexing the neck is primarily the role of other muscles in the neck and upper back, while supporting the pelvic girdle is not related to the trapezius but more associated with muscles in the lower back, pelvis, and hips. Thus, the primary function of the trapezius muscle revolves around stabilizing the shoulder blades and facilitating movement in the upper body.