During inhalation,
a) the volume of the thoracic cavity decreases.
b) the diaphragm and rib muscles contract.
c) air moves up the trachea. the diaphragm relaxes.
d) oxygen molecules move into the lungs, and carbon dioxide molecules move out of the lungs.

B) The diaphragm and rib muscles contract

Explanation:

Inhalation is the activity of breathing,involving or  taking air and sometimes other substances into your lungs.  

Inhalation is a process of breathing in, which involves taking the air inside the lungs. When the person breath in, or inhale, the diaphragm contracts and moves downward. This results in increase in space of the cavity of chest, which facilitates the expansion of the lungs. The intercoastal muscles present between the chest cavity and the ribs also help in enlargement of the chest cavity. These muscles contracts and pulls the rib cage both outward and upward when the person inhales.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products

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