Suppose that the graph illustrates the marginal benefits and costs of cell phone use. S(MC_private) reflects the private marginal costs of cell phone use and S(MC_social) represents the social marginal costs of cell phone use. D(MB) represents the marginal benefits of cell phone use. In the absence of government intervention cell phone use will be 

a. 60 minutes per person per month. 

b. 70 minutes per person per month. 

c. 80 minutes per person per month. 

d. 90 minutes per person per month.

e. Between 70 and 80 minutes per person per month.