GMAT Critical Reasoning (CR) | Re: Rainforests produce a large percentage of the Earth s supply

option A is the clear weakener - if oxygen produced by rainforests is consumed by bacteria and animals living in those forests then it is probably not whole of the earth's oxygen-dependent lives problem
option B is partially true and somewhat out of scope because it provides alternate reasoning but takes the reasoning off topic by mentioning upper atmosphere
option C is a clear strengthener
option D states a fact or a missing premise but doesn't help in weakening so eliminate
option E is also
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