Explanation
In this question, we're asked for the primary purpose of
the passage. We already know this: it's to propose the "radical measure" to
fight water scarcity. That's (B). Meanwhile, (A), (C), and (D) all suffer from
a similar defect in that they describe something that has been discussed, but
which is only a part of the subject of the passage, not a summary of it. In
(A), infrastructure is only part of the problem. In (C), incentives are
described without the purpose of those incentives or the problem being solved.
As for (D), in the passage the notion that government and corporations will
partner is alluded to, but proposing such a partnership isn't the purpose of
the passage; we don't get much description of how they will partner, for
example. Choice (E) is out because "traditional efforts" have not been
described at all in the passage--we don't even know what they are, from the
passage.
The correct answer is (B).
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