Commentator: Although the present freshwater supply is adequate for today's patterns of water use, the human populat...

shunhe on January 1, 2020

Hi @Liam,

Let's trying negating (C) and (D) and see what happens, which is one great way of seeing if an answer choice is an assumption or not. Let's say that the opposite of (C) is true. If the freshwater supply does increase sufficiently to meet the increased needs of humankind, then why would we need the water restrictions? Ex hypothesi, we have enough water to meet humankind's needs. (C) is clearly needed by the argument here.

If we negate (D), on the other hand, we get that some attempts to synthesize water will have an appreciable effect on the quantity of freshwater available. But "an appreciable effect" might not be enough to satisfy all of humankind's needs, and in that case, we would still need water restrictions. Negating (D) doesn't destroy the argument, and so (D) cannot be the correct answer. Hope this helps!