External respiration is the exchange of respiratory gases between the organism and it takes place via a membrane with thin internal respiration is the exchange of gases between and the

External respiration is the exchange of respiratory gases between the organism and the outer environment. 

It takes place via a respiratory membrane with thin moist epithelial cells.

Internal respiration is the exchange of gases between blood and the cells.

The process of diffusion of gases (oxygen and carbon dioxide) in and out of the blood is respiration, internal and external respiration are the types of respiration.

i think the answer is b.

hope it