How does gas exchange occurs when the circulatory and respiratory systems work together

The respiratory and circulatory systems work with each other in this manner, the respiratory system will obtain oxygen then the circulatory system brings the oxygen to different parts of the body then it also takes carbon dioxide from  different tissues of the body and bring carbon dioxide to lungs then the respiratory system takes carbon dioxide outside the body during exhalation

i think it would be b. tissue because an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.

lizards have adapted to life in the desert. some desert lizards have toes with spiny scales to them run across the sand without sinking. some use the sand to hide from predators, or to search for small animals that they prey upon.