#1 - Commentator: Although the present freshwater supply is

[Administrator]

Complete Question Explanation

Assumption—SN. The correct answer choice is (C)

The commentator opens the stimulus with this premise: While today’s freshwater supply is adequate
to meet people’s current needs, during the next few decades there will be an increase in human
population, and a greater need for freshwater.

Based on this premise, the commentator concludes that water use restrictions will soon be necessary
to meet people's freshwater needs. We should note this use of the term “necessary," as it might alert
us to the fact that the commentator uses conditional reasoning in drawing his or her conclusion:

To continue to meet human freshwater needs, water use restrictions will be necessary:

Sufficient Necessary

continue to meet freshwater needs water use restrictions

In other words, if we are able to continue meeting our freshwater needs, that information is sufficient
for us to conclude that water use restrictions have been implemented.

The contrapositive of the statement above tells us that without water restrictions, there is no way to
continue to meet humankind’s freshwater needs in the coming decades:

water use restrictions continue to meet freshwater needs

The stimulus is followed by an Assumption question. In this case, the commentator asserts that
the only way to continue meeting freshwater needs is through water use restrictions. The implicit
presumption is that no other means of achieving this outcome will be effective.

Answer choice (A): The commentator does not discuss humans' wasteful use of other natural
resources, and this assumption is not required by the commentator's argument.

Answer choice (B): The commentator asserts that a drastic population increase in the future will
increase humans' need for freshwater. This argumnet does not rely on any assumptions about the
supply of freshwater in the recent past.

Answer choice (C): This is the correct answer choice. The commentator asserts that water use
restrictions will be an absolute necessity, implying that the problem cannot be solved by any other
means. We can double check our answer to any Assumption question by applying the Assumption
Negation technique: the negated version of the correct answer choice will weaken the author’s
argument.

If we negate (or take away) this assumption from the commentator, we are left with this:
“The freshwater supply will increase sufficiently to meet the increased needs of humankind.”

So, when we take away this assumption from the commentator, the argument fails, proving that this
choice does provide an assumption that the commentator relies upon, and confirming this as the
correct answer choice. We might also note the use of conditional language ("sufficiently")in this
choice. In asserting that water use restrictions are necessary, the commentator implicitly asserts that
no other means would be sufficient.

Answer choice (D): While this answer choice may look enticing at first, the commentator does
not rely upon this argument. To confirm this point, we can again apply the Assumption Negation
technique, take away this assumption, and note the effect, if any, on the strength of the argument in
the stimulus: The negated version of this choice would say that “some attempt to synthesize water
may have an appreciable effect on the supply.” But does this cause the commentator's argument to
fail? No; even if there were an appreciable increase from water synthesis, water use restriction might
still be necessary (above and beyond any synthesis-based increases).

Answer choice (E): Like incorrect answer choice (B) above, this choice is only about the past, and is
not an assumption required by the commentator’s conclusion. Once again, if we wish to confirm this
choice to be incorrect, we can apply the Assumption Negation Technique: the negated version of this
choice ("some measure previously yielded an increase...") this does not weaken the commentator's
argument, which regards only future human needs.