Self-study
Support Recent unexpectedly heavy rainfalls in the metropolitan area have filled the reservoirs and streams; Conclusion water rationing, therefore, will not be necessary this summer.
Summarize Argument
The author concludes that water rationing won't be needed this summer in a particular metropolitan area. In support, the author explains that heavy rain has recently filled the reservoirs and streams in the area. The author is making an argument about cause and effect, claiming that the full reservoirs and streams will cause the area not to need water rationing.
Although the link between full reservoirs and streams and plentiful water in the metropolitan area may seem intuitive, the argument relies on assumptions. Specifically, the author has to assume that this plentiful supply is sufficient to eliminate the need for rationing.
Objective: Weaken
If we can undermine the author's assumption, that lets us weaken the argument.
An answer choice undermining an assumption this broad could come in different forms. For example, the correct answer could tell us that the metropolitan area uses so much water that the extra rain simply wouldn't be enough, but it could also say that the water currently in the reservoirs and streams won't last until the summer, or many other possibilities. So we should keep an open mind and focus on the effect each answer choice has on the argument.
6.
Which one of the following, ██ █████ ████ ██████████ ███ ██████████ ███████████
a
Water rationing was ███████ ██ ███ ████ ██ █████ ██ ███ ████ ████ ██████
So water rationing is sometimes used, but (A) doesn't explain what factors determine whether the area rations water. This means we can't compare the years with and without rationing to this year, which has unusually heavy rains. (A) doesn't challenge the author's assumption so doesn't weaken.
b
A small part ██ ███ ████████ █████ ██████ ██ ████████ ████ ████ ███████████ █████ ███████ ████ ███ ███ ███████ ██ ██████████
In other words, some (small) part of the water supply isn't affected by the extra rain this year. That's fine, but (B) doesn't give us any reason to believe the rain won't still prevent water rationing. Even if not all of the area's water comes from reservoirs and streams, abundant water from those sources could still be enough that the area doesn't need rationing.
c
The water company’s ████████ ██ ████ █████ ██ █████████ ███ ███ ████ ██ ████ ███ █████████ ██████ ███████ ██ ██████████ ██████ ██ ███ ████████████ █████
(C) introduces a new factor that disrupts the author's assumption, thereby weakening the argument. By adding water pumping as a limiting factor on the water supply, (C) tells us that even if the reservoirs and streams are full, that doesn't necessarily mean that water will reach customers. So the rain might not be enough to prevent rationing, if the outdated pumping system just can't transport that water.
d
The long-range weather ████████ ████████ ██████████████████ ████████████ ███ ████ ███████
We don't know what effect the temperature has on water usage or the water supply to the area, so (D) doesn't affect the argument. If we assume that lower temperatures mean less water use, then (D) could even strengthen—but we don't know enough to make that assumption. What we do know is that (D) doesn't weaken.
e
In most years ███ ████ ████████ ████ █████ █████████████ ██ ███ ██████ ████ ██ ████████ ██ ███ █████ ███████
The first problem with (E) is that it makes a general statement which might not even apply to the year in question. (E) is just talking about "most" years, but we already know that there's unusually heavy rain at the moment. That alone is enough to eliminate (E), because we can't judge how it affects this specific year.
The second problem with (E) is that it discusses precipitation relative to season, but we care about precipitation relative to the area's needs (if precipitation is the key factor at all). Even though the summer might get less rain, that could still be enough for the area not to ration water. Conversely, if demand is extremely high, even a lot of rain could be insufficient. Because (E) doesn't give us this context, it wouldn't weaken even if it applied to this specific year.