If a reaction system has come to equilibrium, the concentration of products can be increased
a.
only if it is not reversible.
c.
by applying le châtelier’s principle.
b.
only if the temperature is low enough.
d.
under no circumstances.

If a reaction system has come to equilibrium, the concentration of products can be increased by applying Le Châtelier’s principle. The answer is letter C. The statements "only if it is not reversible",  "only if the temperature is low enough" and "under no circumstances" do not answer the question above.

They carry out the exchange of gases as we breathe ( oxygen and carbon dioxide).