The conclusion of the argument is: "Harvesting trees from old-growth forests for use in manufacture can reduce the amount of carbon dioxide in the atmosphere..." Our premises are: "since when large old trees die in the forest they decompose, releasing their stored carbon dioxide," and there would be more room for new trees that "absorb more carbon dioxide from the atmosphere than do the trees in old growth forests."
(A) is incorrect because it does not address the issue of reducing carbon dioxide in the atmosphere. Though (A) does not present a favorable situation, it is not relevant to the point at hand in the stimulus, which is whether harvesting old-growth trees for use in manufacture will reduce the amount of carbon dioxide in the atmosphere.
(B) is CORRECT because if a lot of the organic matter from old-growth trees is made into products that decompose rapidly, then the carbon dioxide stored in the tree will still be released, which weakens the conclusion because then harvesting trees from the old-growth forests for manufacture would not have the desired effect on the amount of carbon dioxide.
(C) is incorrect because it doesn't matter how much carbon dioxide is stored in the young tree. We are trying to see which answer choice weakens the argument that harvesting old trees will diminish the amount of carbon dioxide in the atmosphere. The fact that young trees have less than half the amount of carbon is irrelevant.
(D) is incorrect because we are trying to show that harvesting trees from the old-growth forests for use in manufacture will not necessarily reduce the amount of carbon dioxide in the atmosphere. Therefore, the fact that much of the carbon dioxide present in forests is eventually released when wood and other organic debris decomposes, if anything, seems to strengthen the logging industry official's proposal to reduce CO2.
(E) is incorrect, because it, again, has no bearing on the logging industry official's proposal on whether or not harvesting trees from old-growth forests for use in manufacture can reduce the amount of carbon dioxide in the atmosphere.
I hope that helps! Let me know if you have any other questions!
