Though the OA is B, i would still vouch for D Here is why:
Stem: The Earths resources are depleting fast.
COnclusion: US has to keep consumption at present levels.
B talks about total consumption of US as a percentage of world consumption. If that (not the percentage but the amount of consumtion) is kept constant, it may decrease the percentage of US consumption in comparison to that of the world's but it may not impact the rate of depletion of earths resources as a whole. What if the rest of the world decides to follow US way?
D talks about the rest of the world consumption as well. US is keeping the consumption constant and the rest of the world also keeps up with this hence the rate of depletion of earths resources is reduced.
IMO it should be D
Time to play the game...