Oxygenated petrol, although it reduces pollution, causes frequent stalling in poorly maintained automobiles. However, in laboratory tests of automobiles that had been driven 100, 000 kilometers, those that had regularly used oxygenated petrol stalled less than those that had regularly used nonoxygenated petrol. Which one of the following, if true, most helps to explain the results of the laboratory tests described above? ['In conducting the tests, the laboratory used each type of petrol on each type of engine.', 'Drivers whose automobiles regularly exhibit adverse effects from oxygenated petrol generally cease to notice the adverse effects by the time their automobiles have been driven 100, 000 kilometers.', 'The adverse effects from oxygenated petrol can be distinguished from mechanical engine problems in the laboratory tests.', 'Automobile owners who regularly use oxygenated petrol get more frequent engine maintenance because of the adverse effects from the petrol.']