Thanks for the question! So let’s take a look at what this appliance dealer is telling us. We’re told that appliance manufactures commonly change the models without giving them new names. Some people don’t like this, since it makes it hard for consumers to know it’s the same one they read/heard about. But the modifications are improvements. Thus, concludes the arguments, the consumers shouldn’t object to this practice.
Now we’re asked for something that would most seriously weaken this argument. What’s the conclusion? That consumers shouldn’t object. So what should we look for? Something that indicates that consumers should object, something wrong with this practice. Let’s take a look at (D), which tells su that improved versions of appliances typically become available before vendors have stopped selling the older versions of the appliance with the same model name. Well, let’s say this is true. What if a consumer wants the newer model? If the new and old models have the same name, they might accidentally buy the older, and worse, model! And if that’s true, then this confusing practice should probably be stopped. Since (D) weakens the argument, it’s the correct answer.
Hope this helps! Feel free to ask any other questions that you might have.