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Typically during thunderstorms most lightning strikes carry a negative electric charge; only a few carry a positive charge. Thunderstorms with unusually high proportions of positive-charge strikes tend to occur in smoky areas near forest fires. The fact that smoke carries positively charged smoke particles into the air above a fire suggests the hypothesis that the extra positive strikes occur because of the presence of such particles in the storm clouds.
Which of the following, if discovered to be true, most seriously undermines the hypothesis?
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| Typically during thunderstorms most lightning strikes carry a negative electric charge; only a few carry a positive charge. |
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| Thunderstorms with unusually high proportions of positive-charge strikes tend to occur in smoky areas near forest fires. |
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| The fact that smoke carries positively charged smoke particles into the air above a fire suggests the hypothesis that the extra positive strikes occur because of the presence of such particles in the storm clouds. |
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We start with normal lightning patterns, then learn about an unusual situation near fires, and finally get a proposed explanation for why this happens
The hypothesis is that positive smoke particles in storm clouds cause the extra positive lightning strikes near forest fires
The argument uses a pattern of normal vs. unusual observations, then connects the unusual pattern to a specific cause (positive smoke particles) to explain the effect (more positive lightning)
Weaken - We need to find information that would reduce our belief in the hypothesis that positively charged smoke particles cause the extra positive lightning strikes in forest fire areas.
The hypothesis makes a specific causal claim: positively charged smoke particles in storm clouds cause the unusually high proportion of positive lightning strikes near forest fires. We need to respect the facts that positive strikes do increase near fires and that smoke does carry positive particles.
To weaken this cause-and-effect hypothesis, we can attack it in several ways: (1) Show an alternative cause for the increased positive strikes, (2) Show that the proposed mechanism doesn't work as suggested, or (3) Show that areas with similar smoke particle conditions don't produce the same effect. We cannot question the basic facts given - that positive strikes increase near fires or that smoke carries positive particles.
This tells us that other rare lightning types also occur near forest fires. However, this doesn't weaken our specific hypothesis about positive strikes being caused by positive smoke particles. We can have multiple unusual lightning phenomena happening in the same area for different reasons. This is essentially irrelevant information that doesn't challenge the causal relationship we're examining.
The power level of positive strikes doesn't relate to what causes them. Whether positive strikes are more powerful, less powerful, or equally powerful compared to normal doesn't tell us anything about whether smoke particles cause them. This is about the characteristics of the strikes, not their origin, so it doesn't weaken the hypothesis.
This compares the fire-starting ability of positive versus negative strikes. Like choice B, this is about what the strikes can do, not what causes them to occur. The hypothesis is about causation of strike frequency, not about the effects those strikes have on starting fires, so this is irrelevant.
This directly attacks the core causal claim. If thunderstorms in drifting smoke clouds still have extra positive strikes weeks after the smoke particles have lost their positive charge, then those charged particles cannot be causing the extra positive strikes. We have the effect (extra positive strikes) without the proposed cause (positively charged particles), which breaks the causal chain the hypothesis depends on. This makes the hypothesis impossible to sustain.
The total number of strikes staying normal doesn't weaken the hypothesis. We're specifically concerned with the proportion of positive versus negative strikes, not the overall quantity. The hypothesis explains why we get more positive strikes as a percentage, and this choice doesn't address that relationship at all.