The Following Data Show the Relationship Between the Number of Drivers

The following data show the relationship between the number of drivers who leave for work at 8:00 am,their average commute times,and their marginal benefit associated with the commute times. $$\begin{array} { c c c } \begin{array} { c } \text { Number of drivers } \\ \underline {\text { that leave at 8:00am }}\end{array} & \begin{array} { c } \text { Average commute } \\ \underline {\text { time to downtown }}\end{array} & \begin{array} { c } \text { Marginal } \\ \underline {\text { Benefit }}\end{array} \\ 100 & 30 \text { minutes } & \$ 10 \\200 & 65 \text { minutes } & \$ 8 \\300 & 110 \text { minutes } & \$ 4 \\400 & 170 \text { minutes } & \$ 3 \\500 & 260 \text { minutes } & \$ 1\end{array}$$
Refer to the information given above.Suppose a toll is imposed in the following way: leaving between 8 a.m.and 9 a.m.costs $5 per driver,after 9 a.m. ,the toll is zero.The toll __________ because __________.

A) reduces efficiency;citizens are paying for the highway through taxes and through the toll
B) improves efficiency;government now has more tax revenue
C) reduces efficiency;drivers don't change their behavior because $5 is less than the benefit of driving
D) improves efficiency;the highway is no longer treated as having a price of zero