the circulatory system transports blood throughout the body0 & the absorption of oxygen through the blood occurs in the lungs ->  the lungs bring in oxygen from the air  the lungs bring in oxygen from the air & bringing oxygen to the body is a kind of function ->  the lungs perform the function of bringing in oxygen from the air  the lungs are a part of the respiratory system & if a part of a system performs a function then that system performs that function through that part ->  if the lungs perform a function then the respiratory system performs that function through the lungs  the lungs perform the function of bringing in oxygen from the air & if the lungs perform a function then the respiratory system performs that function through the lungs ->  the respiratory system takes in oxygen from the air through the lungs  the respiratory system transfers oxygen to the circulatory system & to transfer something somewhere can mean to bring something somewhere ->  the respiratory system brings oxygen to the circulatory system  the respiratory system takes in oxygen from the air through the lungs & the respiratory system brings oxygen to the circulatory system ->  the respiratory system brings oxygen from the air to the circulatory system  the circulatory system transports blood throughout the body & blood is a vehicle for carrying oxygen from the lungs to the rest of the body ->  the circulatory system brings oxygen from the lungs to the rest of the body  the respiratory system brings oxygen from the air to the circulatory system & the circulatory system brings oxygen from the lungs to the rest of the body ->  the respiratory system and the circulatory system both work to bring oxygen from the air to the rest of the body  if two things perform the same function then those two things are similar & bringing oxygen to the body is a kind of function ->  if two things both bring oxygen to the body then those two things are similar  the respiratory system and the circulatory system both work to bring oxygen from the air to the rest of the body & if two things both bring oxygen to the body then those two things are similar -> the respiratory system and circulatory system are similar because they bring oxygen to the body