Rightly so :
This seems like a tricky SC to me. Since in the comprehension & subsequent answers there is insinuation towards choosing answers C or D. Thats what supports the RC passage most.
But that seems to be a trap. Since statement E if you compare C, D & E. E provides the most low profile, however better justification to profits.
They Key is Profits "Substantially higher". Since sales of number of models remained the same & prices didn't go up. The only thing that could have led to substantially higher profits is "Low Production Cost".
Why not C & D. This is where the argument C & D fail. Since they talk about most plausible reasons over a false impression. Which is stated at the start of the paragraph. Which is "PXC's first time buyer give comparatively lower profits then PXC second time". However it doesn't qualitatively tell us how much more. if these are not more and we sold the same amount of PXC's with similar profit margins, profits
cannot be significantly higher.
Let me know if the explanation helps?