Question ID:PT29 S1 Q24 Passage:Automobile-emission standards are enforced through annual inspection.  At those inspections cars are tested while idling; that is, standing still with their engines running.  Testing devices measure the levels of various pollutants as exhaust gases leave the tail pipe. Stem:Which one of the following, if true, most strongly indicates that current enforcement of automobile-emission standards might be ineffective in controlling overall pollutant levels? Correct Answer Choice:CChoice A:As an emission-control technology approaches its limits, any additional gains in effectiveness become progressively more expensive. Choice B:The testing devices used must be recalibrated frequently to measure pollutant levels with acceptable accuracy. Choice C:The adjustments needed to make a car idle cleanly make it likely that the car will emit high levels of pollutants when moving at highway speeds. Choice D:Most car owners ask their mechanics to make sure that their cars are in compliance with emission standards. Choice E:When emission standards are set, no allowances are made for older cars.