If household expenditure on electricity remainsconstant when the price of electricity increases, the price elasticity ofdemand for electricity is a

a.One (in absolute value). (Because the total expenditure isconstant, so %P= - %

b.Zero.

c.Greater than one (in absolute value).

d.Less than one (in absolute value).

e.Cannot be determined.

正确答案是A

但是我不懂，我觉得是他的弹性应该是0？因为弹性公式是q的变化量的百分比比上p的变化量的百分比，题目中不管价格怎么变，数量永远不变，所以弹性应该是0啊？

谢谢！