The Formula for the Arc Elasticity of Demand Can Be $\eta$

The formula for the arc elasticity of demand can be written as:

A) $\eta$ _XY = [ $\Delta$ Q_X /(Q¹_X + Q²_X) ]/[ $\Delta$ _X/(P¹_X + P²_X) ].
B) $\eta$ _XY = [ $\Delta$ Q_X /(Q¹_Y + Q²_Y) ]/[ $\Delta$ _Y/(P¹_X + P²_X) ].
C) $\eta$ _XY = [ $\Delta$ Q_X /(Q¹_X + Q²_X) ]/[ $\Delta$ P_Y/(P¹_Y + P²_Y) ].
D) $\eta$ _XY = [ $\Delta$ P_X /(P¹_X + P²_X) ]/[ $\Delta$ Q_Y/(Q¹_Y + Q²_Y) ].
E) none of the above.