Every Time You Go to the Grocery Store, You Try

Every time you go to the grocery store, you try to choose the shortest line. But all of the lines always seem to be the same length. Why?

A) The store manager tells the cashiers to speed up or slow down to maintain equal line lengths.
B) Everyone else is trying to choose the shortest line too.
C) The cashiers all work at the same speed.
D) Cashiers do not have an incentive to work faster.