Certainly, pesticides can adversely affect the environment in localities distant from where the pesticide has actually been used. Nevertheless, regulation of pesticide use should not take place at the national level but at the local level. It is in the areas where pesticides are actually applied that they have their most serious effects. Just how serious these effects are depends on local conditions such as climate, soil type, and water supply. And local officials are much more likely than national legislators to be truly knowledgeable about such local conditions.

In the argument given, the two boldface portions play which of the following roles?