Summarize Argument: Phenomenon-Hypothesis
The author hypothesizes that the main cause of the declining amphibian population is the depletion of the ozone layer. This is based on the following facts. First, the ozone layer has been continuously depleted over the last 50 years. Second, ozone blocks UV-B, to which amphibians are vulnerable due to their lack of hair/hide/feathres and because their eggs lack leathery/hard shells.
Notable Assumptions
The author assumes there’s no more significant causal factor for the declining amphibian population than the declining ozone layer.
A
Of the various types of radiation blocked by atmospheric ozone, UV-B is the only type that can damage genes.
This tells us that there are other types of radiation blocked by atmospheric ozone. But if these other types don’t damage genes, there’s no reason to think they play a role in damaging amphibians. So, there’s no clear impact.
B
Amphibian populations are declining far more rapidly than are the populations of nonamphibian species whose tissues and eggs have more natural protection from UV-B.
This provides evidence that the lack of protection to UV-B is helping to cause amphibian populations to decline.
C
Atmospheric ozone has been significantly depleted above all the areas of the world in which amphibian populations are declining.
This strengthens the connection betwen ozone depletion and declining amphibian populations.
D
The natural habitat of amphibians has not become smaller over the past century.
This strengthens by eliminating an alternate explanation for the declining amphibian population. If the natural habitat had been getting smaller, that could have been the main reason amphibians are dying off. (D) eliminates this possibility.
E
Amphibian populations have declined continuously for the last 50 years.
Since we’re told the ozone depletion has been occurring “continuously” over the past 50 years, (E) helps strengthen the connection between the declining amphibian population and the depleting ozone.
Summarize Argument: Phenomenon-Hypothesis
The author hypothesizes that passengers using electronic devices put modern airplanes at risk. Why? Because the planes’ navigation systems use low-power circuitry that’s more susceptible to interference than vacuum-tube circuitry in old planes, as illustrated by a recent incident where a navigation system apparently malfunctioned when a passenger opened a laptop.
Notable Assumptions
The author assumes the navigation system’s behavior during the off-course landing was unusual and occurred because the passenger opened their laptop, and not for some other reason. This means assuming laptops and cassette players carried by passengers produce radiation that’s capable of interfering with a modern navigation system.
A
After the laptop computer was turned off, the plane regained course and its navigation instruments and dials returned to normal.
This strengthens the argument by making it more likely the laptop caused the navigation system’s behavior during the off-course landing.
B
When in use all electronic devices emit electromagnetic radiation, which is known to interfere with circuitry.
This strengthens the argument by confirming that cassette players, laptops, and other devices produce radiation. It rules out the possibility that some electronic devices emit no radiation, which would weaken the argument.
C
No problems with navigational equipment or instrument dials have been reported on flights with no passenger-owned electronic devices on board.
This strengthens the argument by ruling out a powerful counterexample. If similar behavior had occurred on flights with no passenger-owned devices, then the laptop’s responsibility would be less likely.
D
Significant electromagnetic radiation from portable electronic devices can travel up to eight meters, and some passenger seats on modern aircraft are located within four meters of the navigation systems.
This strengthens the argument by confirming that passengers sit close enough for radiation from their devices to reach navigation systems. If all the passengers sat too far away for their radiation to reach those systems, the argument would falter.
E
Planes were first equipped with low-power circuitry at about the same time portable electronic devices became popular.
This is irrelevant. The author concludes there’s a risk presently—it doesn’t matter when passenger-owned devices and low-power circuitry became prevalent, so long as they’re both prevalent right now.
Summarize Argument: Phenomenon-Hypothesis
The official hypothesizes the new pesticide better protects some fruit against insect pests than the old pesticide, at least in the short term. Why? Because when the new pesticide was applied to a sample of pear trees over three years, those trees lost fewer pears to insects than they had over the previous three years.
Notable Assumptions
The official assumes there’s no other reason, besides the new pesticide, why insects ate a smaller proportion of the sample pears during the last three years than they ate during the previous three years.
A
peach trees grown in the district that were treated with the new pesticide instead of the old pesticide
This would neither strengthen nor weaken the official’s argument. He restricts his conclusion to “certain” fruits, so it would not affect his argument if peaches did worse than pears.
B
peach trees grown in the district that were treated with the new pesticide in addition to the old pesticide
This would neither strengthen nor weaken the official’s argument. He makes no claim about the effectiveness of the new pesticide when used in tandem with the old pesticide.
C
pear trees grown in the district that were treated with the old pesticide instead of the new pesticide
This strengthens the official’s argument. It implies pear trees treated with the new pesticide showed more resistance to insects than those treated with the old pesticide during the same time.
D
pear trees grown in a neighboring district that were treated with neither the old nor the new pesticide
This is irrelevant to the official’s argument. He makes no claim about the ability of untreated trees to keep their fruits safe from insects.
E
pear trees grown in a neighboring district that were treated with the new pesticide instead of the old pesticide
This slightly weakens the official’s argument—it doesn’t strengthen it. It suggests factors specific to District 10 could have been responsible for fewer pears being eaten by insects.
Mary: There are already too few part-time jobs for students who want to work, and simply requiring students to work will not create jobs for them.
Summarize Argument: Counter-Position
In response to Tom’s claim that high school students should be required to work part-time jobs, Mary points out that there are few part-time jobs available for students and a requirement to work will not create jobs.
Describe Method of Reasoning
Mary counters the position held by Tom. She does this by weakening a crucial assumption in Tom’s argument: that part-time jobs exist for students required to work them. By pointing out that there are already too few part-time jobs and that jobs will not be created by simply requiring students to work, Mary implies that high school students should not be required to work part-time jobs.
A
It analyzes an undesirable result of undertaking the course of action that Tom recommends.
Mary does not mention what would happen if students were required to work part-time jobs. Rather, she emphasizes the impossibility of instituting the requirement in the first place.
B
It argues that Tom has mistaken an unavoidable trend for an avoidable one.
Mary does not state that the trend of high school students graduating without vocational skills is unavoidable. Rather, she argues that Tom’s solution to the trend is not a viable solution.
C
It provides information that is inconsistent with an explicitly stated premise in Tom’s argument.
Mary does not provide information that contradicts the fact that employers are complaining or that vocational skills are best acquired on the job.
D
It presents a consideration that undercuts an assumption on which Tom’s argument depends.
The assumption Tom’s argument depends on is the assumption that part-time jobs are available for students if those students were required to work. Mary undercuts this assumption by pointing out that too few of these jobs exist to fulfill this requirement.
E
It defends an alternative solution to the problem that Tom describes.
Mary does not propose an alternative solution to the problem. Her argument is limited to addressing Tom’s proposed solution.