If some forms of "stress" (adding, removing, heating, cooling, changing volume) is applied to the exothermic reaction, 2 CO(g) + O2(g) ⇋ 2 CO2(g), when it is at equilibrium, then a change will occur in the concentration(s) of
a. products only
b. neither reactants nor products
c. both reactants and products
d. reactants only
e. need to know which "stress"