This system works with the circulatory system to provide this oxygen and to remove the waste products of metabolism. It also helps to regulate pH of the blood. A. Endocrine system B. Cardiovascular System C. Reproductive System D. Respiratory System

D. Respiratory System<br /><br />The respiratory system works in conjunction with the circulatory system to deliver oxygen to the body's tissues and remove carbon dioxide, a waste product of metabolism. It also plays a role in regulating blood pH.<br />