Which of the following is NOT a body system?

The correct answer identifies the glandular system as not being classified as a standalone body system. Instead, the glandular functions are typically associated with the endocrine system, which comprises glands that secrete hormones and regulate various body processes. The term 'glandular' can refer to specific functions of these glands but is not recognized as a distinct body system on its own.

In contrast, the cardiovascular system is responsible for the circulation of blood and transportation of nutrients and oxygen throughout the body. The nervous system plays a crucial role in transmitting signals between different parts of the body, facilitating communication and coordination of bodily functions. The muscular system includes all muscles in the body that are involved in movement and maintaining posture. All of these, unlike the glandular functions, are classified as essential and distinct systems that play significant roles in human physiology.