The city of Workney, in raising bus fares from $1.00 to $1.25, proposed that 18 fare tokens be sold for $20.00 to alleviate the extra burden of the fare increase on the city's low-income residents. Critics suggested alternatively that 9 fare tokens be sold for $10.00, because a $20.00 outlay would be prohibitive for low-income riders.

The alternative proposal depends on which of the following assumptions?

【选项】Buses provide the only means of public transportation in the city of Workney.