Suppose leisure is on the horizontal axis and dollars are on the vertical axis in the consumer-choice diagram. What happens to the budget line when a head tax is imposed?

a. The budget line shifts inward, but it may become steeper or flatter depending on the size of the head tax.

b. The budget line pivots about the horizontal intercept, becoming steeper.

c. The budget line become flatter, with the vertical intercept falling and the horizontal intercept remaining fixed.

d. There is an inward, parallel shift in the budget line.

d. There is an inward, parallel shift in the budget line.