Why not answer choice E?

The problem with E is when it says, "In some Zenith cars, a minor part has broken." This doesn't have anything to do with whether or not a test drive actually causes someone to purchase a car in the first place, so we can take this one out. With C, the key words are "have already decided to buy the model." If they've already made the decision to buy the car, then the test drive has no effect on their decision to buy it. This really weakens the notion that the test drive actually caused people to buy the car, so this is the correct choice.

I understand your reasoning and that is why for me answer C was also my second choice, however, the question stem is specifically referring to the quality of that car and in answer choice E, they specifically say that their is a defect. So I think I am still slightly confused about why E would not have been a better answer.

Hi, I don't think that E disproves the idea that the car is of high quality. The fact that some (which could mean as few as one) have developed a minor issue which the company has noticed and taken responsibility for does not mean that the car is not unusually high in quality. There is no product that is 100% perfect all of the time. More importantly, this has nothing to do with the argument. We are looking to weaken the argument, which is about test driving.