Which of the Following Formulas Is Used to Calculate the Arc

Which of the following formulas is used to calculate the arc elasticity of demand?

A) Arc elasticity of demand = [(Q₂ − Q₁) /(Q₂/2) ]/[(P₂ − P₁) /(P₂/2) ]
B) Arc elasticity of demand = [(Q₂ + Q₁) /(Q₂/2) ]/[(P₂ + P₁) /(P₂/2) ]
C) Arc elasticity of demand = [(Q₂ − Q₁) /(Q₂ + Q₁) /2]/[(P₂ − P₁) /(P₂ + P₁) /2]
D) Arc elasticity of demand = [(Q₁ − Q₂) /(Q₂ + Q₁) ]/[(P₁ − P₂) /(P₂ + P₁) ]