Read the following passage and choose the option that cannot be said to be an implicit assumption:

The pollution level in the city has skyrocketed in the past few months. The city corporation, in an attempt to curb the pollution, has made it mandatory for all vehicles to be fitted with catalytic converters. Also, it has proposed a policy by which only vehicles of a particular parity (odd or even numbered vehicles) can be driven on a particular day.

The steps to curb pollution mainly addresses the vehicular pollution. Therefore, vehicles must be one of the major contributors to pollution level in the city. Since the corporation wants the people to install catalytic converters, we can infer that catalytic converters can reduce the emission levels. Also, the corporation proposes to allow vehicles of only a particular parity on a day. Therefore, the corporation thinks that this will force people to adopt alternative modes of transport to reach their destination. Also, the corporation puts down all the rules with a belief that the citizens will implement it. All options from B, C, D and E are implicit assumptions on which the rule has been made. 

Just because the pollution control measures address vehicular pollution, we cannot say that the pollution from other sources are negligible. Vehicular pollution can be the major contributor, but it does not necessarily mean that the other sources will not have significant share. Therefore, option A cannot be said to be an implicit assumption and hence, option A is the right answer.