PrepTest 154, Section 2, Question 21
A study of 30 years of weather pattern(50 more words not shown)
Which one of the following(8 more words not shown)
- AIndustrial activity tends(12 more words not shown)
- BThere are no(8 more words not shown)
- CIf living organisms(21 more words not shown)
- DIf something appreciably(10 more words not shown)
- EIf a weather(16 more words not shown)
Reading the argument
Why would the weekend be cloudier? The calendar is something people use, so a pattern following it makes human activity a plausible place to look. Perhaps traffic or some other weekly activity affects the clouds. But we need to see what the argument actually establishes.
My first reaction is to question the size of the result. How much cloudier?
Does the difference really justify calling the effect appreciable and large-scale? A barely noticeable difference would raise a different question from a dramatic change. The author gives us a thirty-year pattern but doesn't spell out the size of the difference.
The offered reason for blaming human activity is that naturally occurring seven-day cycles are too insignificant to produce measurable weather patterns. The author is trying to rule out a natural explanation and leave human activity as the cause.
What we’re looking for
For the required assumption, we should test what that exclusion depends on. I initially focused on the size of the effect, but the choices may reveal another connection the argument needs. We want something the author must accept for this reasoning to work, not a particular guess about which human activity is responsible.
Working the answers
- A
Human activity is broader than industrial activity. A weekly difference could involve travel or recreation rather than factories. The argument doesn't need industrial activity to decrease on weekends; it needs human activity to explain the pattern somehow. A picks a specific mechanism the author hasn't committed to.
- B
The argument doesn't need natural seven-day cycles to be absent. Its premise already says the few that occur naturally are too insignificant to cause measurable weather patterns. Being unable to explain the observed effect is enough for the author's intended exclusion; complete nonexistence would be stronger than necessary.
- C
This gives a broad rule about all appreciable weather effects caused by living organisms. The argument only needs to explain this particular weekly pattern. It could allow some other organism to affect weather independently of humans without giving up its proposed explanation here.
- D
The author doesn't need every substantial influence on weather to be cyclical. Some other event could affect weather without following a repeating schedule. The reasoning concerns the cause of one observed cycle, not a rule governing all causes of weather changes.
- ECorrect
This exposes a connection I hadn't focused on: does a seven-day effect require a seven-day natural cause? The author rules out natural causes with seven-day cycles. That works only if a natural explanation of the weekly cloud pattern would itself have that schedule.
Suppose a natural process with a different schedule could nevertheless produce a seven-day weather pattern. Then saying natural seven-day cycles are too weak would leave that explanation untouched. E closes this gap. It doesn't prove which human activity causes the clouds; it is needed to make the author's dismissal of natural explanations work.
More Necessary Assumption questions
Learn the LSAT our way
Our platform drills Necessary Assumption questions at your level and adjusts as you improve.