I've never made a comment on an LSAT question before but I wholeheartedly believe B) is the wrong answer and A is better. It comes down to "significantly reduces". As other people have mentioned, you can use up something faster (even MUCH faster) than it can be replaced without 'Significantly' reducing it, at least at the moment or while its happening. if B had 'eventually' tacked on or didn't have 'significantly', it would have, unequivocally, been the best answer, but it doesn't so its not. I care so much about this because the really difficult level 5 questions (with around a 30% correct answer rate) all hinge on being really clinical on what sorts of assumptions we're allowed to make. then you have this question that only works if you can randomly divine the mechanics of a hypothetical oxygen cycle that exist in the test constructors mind.

just chiming in to say I feel the exact same way