单项选择题

The number of times per minute that you breathe is ______.

A．fixed at twenty-two times per minute
B．influenced by your age and sex
C．dependent upon the amount of fresh air available to you at any given time
D．controlled automatically by an unspecified body mechanism

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热门试题

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

While air is in the lungs, it changes in the following way: ______.

A．Nitrogen is absorbed from the air
B．About one-fifth of the carbon dioxide and about one-half of the oxygen in the air goes into the blood
C．The moisture in the air is almost completely evaporated
D．About one-fifth of the oxygen in the air goes into the blood and an equivalent amount of carbon dioxide enters the air from the blood