I believe the OA should be D. I also believe that this question sucks.
"A study of the real estate industry, however, revealed that the current supply of homes could only provide for 65% of that demand each year."
Here, "that" is clearly referring to the 85% of the magazine's readers. It's not saying that the industry can only provide for 65% of the nation's population, but that it can only provide for 65% of the readers. Therefore, the statistic is completely representative of the market.
For simplicity's sake, let's use real numbers:
Assume that there are 100 magazine readers. 85 want a second home. The industry can only provide 55 houses. Obviously there is still a shortage, and investing in real estate can still be a good idea.
...Stupid GMAT; it tests anaphors in SC, but can't even create a proper antecedant in CR. :roll: