The correct answer is: B. Equal to one
The elasticity of demand is a measure of how responsive
consumers are to changes in price. It is calculated by dividing the percentage change in quantity demanded by the percentage change in price.A straight demand line has a constant elasticity of demand. This means that the percentage change in quantity demanded is always equal to the percentage change in price.
The elasticity of demand at the midpoint on a straight demand line is equal to one. This is because the percentage change in quantity demanded is equal to the percentage change in price at the midpoint.
Option A is incorrect because the elasticity of demand at the midpoint on a straight demand line is not equal to zero.
Option C is incorrect because the elasticity of demand at the midpoint on a straight demand line is not greater than one.
Option D is incorrect because the elasticity of demand at the midpoint on a straight demand line is not less than one.