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A．to
B．with
C．on
D．for
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单项选择题The process by which carbon dioxide and oxygen are transferred does not depend on_______.

A．the presence of nitrogen in the blood
B．the muscles of the thoracic cavity
C．the flow of blood
D．the moisture in the air sac linings

单项选择题In the respiratory process, the following action takes place:_______.

A．Diffusion of blood through capillary walls into air sacs
B．Exchange of alveoli and oxygen within air sacs
C．Diffusion of oxygen through the air sac and capillary walls into the blood
D．None of the above