Why has that revenue source not grown fast enough to deliver an efficient scale of infrastructure provision?

The revenue source has not grown fast enough to deliver an efficient scale of infrastructure provision because

A$.$ the number of bridges and roadways is increasing at a faster rate than the number of drivers

B$.$ as cars become more fuel efficient, they use less gas and the fuel tax generated decreases

C$.$ more and more ethanol is being added to gasoline and tax is not imposed on ethanol

D$.$ more people are commuting in groups, so they use less gas and the fuel tax generated decreases