In order to reduce traffic congestion and raise revenue for the city, the mayor plans to implement a charge of $10 per day for driving in the downtown area. Payment of this charge will be enforced using a highly sophisticated system that employs digital cameras and computerized automobile registration. This system will not be ready until the end of next year. Without this system, however, mass evasion of the charge will result. Ttherefore, when the mayor' s plan is first implemented, payment of the charge will not be effectively enforced. Which one of the following is an assumption on which the argument depends for its conclusion to be properly drawn? ["The mayor's plan to charge for driving downtown will be implemented before the end of next year.", 'A daily charge for driving downtown is the most effective way to reduce traffic congestion.', 'The plan to charge for driving downtown should be implemented as soon as payment of the charge can be effectively enforced.', 'Raising revenue is a more important consideration for the city than is reducing traffic congestion.']