If You Have Already Signed Up for a Plan with Your

Multiple Choice

If you have already signed up for a plan with your cell phone company that gives you 4,000 free minutes for $39.99 per month with a cost of $0.35 per minute for any time exceeding the limit, your marginal cost curve is:

A) horizontal at a marginal cost of zero.
B) horizontal at a marginal cost of zero up to 4,000 minutes.
C) horizontal at a marginal cost of $0.35.
D) upward-sloping.