Determine the condition that will increase the amount of C₄H₈Br₂ at equilibrium for the endothermic reaction: 
C₄H₈ (g) + Cl₂ (g) ⇌ C₄H₈Br₂ (g)
a. removing Cl₂ from the mixture
b. increasing the volume of the reaction
c. increasing the amount of C₄H₈
d. increasing the temperature of the reaction