What system consists of the heart, blood, and blood vessels?

The cardiovascular system is the correct answer because it specifically includes the heart, which pumps blood, the blood itself, which transports nutrients and oxygen, and the blood vessels, which carry blood throughout the body. This system is crucial for maintaining circulation, delivering essential substances to cells, and removing waste products.

In contrast, the endocrine system focuses on hormone production and regulation of various bodily functions, while the digestive system is responsible for the breakdown and absorption of food. The nervous system, on the other hand, controls bodily functions through electrical signals, coordinating reactions and responses. Each of these systems plays a vital role in the body, but it is the cardiovascular system that directly encompasses the heart, blood, and blood vessels.