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【单选题】
Inhalation of air into the lungs is correctly described by which of the following?A.
the action of the diaphragm and the ribs create a positive pressure in the thoracic cavity which causes air to move into the lungs.
B.
the volume of the thoracic cavity is increased as muscles relax, thus increasing the pressure and air is forced into the lungs.
C.
the thoracic cavity decreases in volume as muscles relax and pressure decreases so external air is forced into the lungs.
D.
the lungs expand as muscles contract, this creates a negative pressure so air is forced into the lungs.
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【判断题】波特认为有5种力量决定整个市场或其中任何一个细分市场的长期的内在吸引力。这5种力量分别是：同业竞争者、潜在的或新加入的竞争者、替代产品、购买者和供应商。
A.
正确
B.
错误