Commentator: Although the present freshwater supply is adequate for

Commentator: Although the present freshwater supply is adequate for today’s patterns of water use, the human population will increase substantially over the next few decades, drastically increasing the need for freshwater. Hence, restrictions on water use will be necessary to meet the freshwater needs of humankind in the not-too-distant future.

MEANING
Present fresh water supply is enough for today's use.
But, over next few decades, human population would increase. The current supply is not enough to meet the increased freshwater requirements.

CONCLUSION = Restrictions on water use is needed to meet demands.

Let's identify what's the gap?
Not enough water............................Need to restrict water use.
Why do we need to restrict water? If water resources increase proportionally with population, clearly the demand would be met and we can continue with today's patterns of water use, without bringing in any restriction whatsoever.
So, the assumption is that water resources won't increase, hence to adjust with existing resources, restrictions are needed.
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CR Bible mentions that there are 2 types of assumptions

• Supporter Assumption : This is used to connect missing link between premise and conclusion.
• Defender Assumption : In case the argument is strong and there is no suitable missing link between premise and conclusion, these type of assumptions protect the argument by eliminating ideas that could weaken the argument.

Since there is a clear gap in the argument, we should go with (C)
(D) is a weak defender assumption, appreciable quantity improvement is not equal to sufficient quantity.
Suppose, present water =100 litres, future requirement =200 litres
Improved water because of synthesizing water =150 litres.
Thus, even though there is an appreciable improvement (50%), that's simply not enough.

Thus, (D) loses out to (C)

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