Question

the circulatory system works closely with the respiratory system to...
regulate body temperature.
pick up carbon dioxide and drop off oxygen waste.
carry the chemical messengers called hormones.
pick up oxygen and drop off carbon dioxide waste.

Explanation:

The respiratory system takes in oxygen and expels carbon - dioxide. The circulatory system then transports oxygen to body cells and picks up carbon - dioxide from them to be exhaled by the respiratory system.

Answer:

pick up oxygen and drop off carbon dioxide waste.