Which of the following "stresses" applied to the following reaction, initially at equilibrium, would decrease the pressure of O2 in the reaction vessel as the system re-establishes equilibrium conditions?

2 CaSO4(s) ⇌ 2 CaO(s) + 2 SO2(g) + O2(g) ΔH° = 1003 kJ

a) Grind the CaSO4 to increase its surface area

b) Decrease the temperature of the reaction vessel

c) Add a catalyst to the reaction mixture

d) Remove CaO from the reaction mixture

e) Add CaO to the reaction mixture