Emmorens,

I understand your intuition of it not being "strong enough". However, one needs to remember that it is very possible to have four answer choices that are essentially nonsense and don't weaken the conclusion, and a single correct answer choice that weakens but... ever so slightly.

That is the sort of situation were in here with this AC. Imagine a situation in which, despite our population growth, were consuming only a small percentage of the available water supply for our needs.

What B is trying to say is that... the availability of water across the globe varies in its degree of availability significantly. Perhaps a hypothetical will capture it a bit better.

Imagine someplace like the United States, where there is an abundance of fresh water available to meet the needs of a growing population. Conversely, imagine someplace of a very different climate, perhaps some places where due to climate, there is quite a severe amount of drought. If a massive spike in population occurs in the former location, human kind there will NOT be plagued by water shortages. However, in the second location, if a massive population surge occurs, there is likely to not be enough water to accommodate such an expansion of population, hence they very may well suffer water shortages!

In summary, answer choice B is pointing out that populations and water supplies are not uniformly distributed across the globe. Populations could expand in a location and have the water supply available to meet such an expansion, however other location may be near the breaking point already.

I would like to join, PT'ing in the 172-180 range.

Intuition would tell me that perhaps were allowed to make that small leap due to the fact that were focused upon books of "intrinsic merit", which more or less translates into books of high quality or... maybe perhaps books whose topic have intrinsic merit. The immediate example that came to my mind was philosophy textbooks.