C

Also, i forgot to add this, but the reason I had crossed out D is because it did not mention that they were looking for the cheaper option. it simply said pine is cheaper... painting it would make it less cheap than cedar. this doesn't imply (like in the original passage) that the person was seeking the more efficient (here cost, in the passage energy) option. the person could really prefer pine as it looks, or how it accepts paint/sealer. let me know what anyone thinks,

Hi Hanfan, I think the biggest difference is the could. C is a straightforward argument, more people means less efficiency. This is not what the initial argument was. The initial argument was saying that this shift to a new thing might be counterproductive. Additionally, you had to insert your own assumptions to make C the same argument, which is not allowed. D is a strong match for our initial argument, it says something could be counterproductive by increasing the total cost in terms of money or energy.