In the past decade, two Motorlux models, the T-300, a sports car, and the AG-75, a sports utility vehicle, have been manufactured with the same timing belt, which controls the timing of the engines valves: when the engine is running at a higher RPM, there is more strain on the timing belt. Recent evidence indicates that this particular brand of timing belt has a usable life of about 135, 000 miles, somewhat less the 200, 000 miles life typical of standard timing belt. Although the same model of timing belt has been used for both models of cars, the incidence of timing belt failure is considerably higher in the AG-75 than in the T-300. This is most likely because __ Which of the following, if true, most logically completes the argument? ['it is common for sports utility vehicles to tow heavy objects, such as motor boats; whereas sport cars almost never tow anything.', 'the timing belts typically used in most other models of sports cars on the market are of higher quality than the timing belts typically used in most other models of sports utility vehicles on the market.', 'where legal, drivers of the T-300 have been known to drive it at speeds in excessive of 100 mph; whereas the AG-75 is rarely driven that fast.', 'timing belts are automatically replaced when the entire transmission systems is repaired or replaced, and, unlike sports utility vehicles, sport cars such as the T-300 tend to experience transmission systems problems before the 100, 000 mile mark.']