Summary
Severing a motor nerve kills part of the nerve. However, the nerve can regenerate. When regenerating, a nerve grows about 1 millimeter every day from the point of severing toward the muscle the nerve controlled. For example, a severed motor nerve controlling a hand would take longer to regenerate if the nerve was severed at the shoulder compared to the wrist. Growing nerve cells require the original nerve sheath to guide them to the muscle that lost function. However, the original nerve sheath disintegrates after three months unless living nerve tissue exists within it.
Strongly Supported Conclusions
If an original nerve sheath has living nerve tissue, then the likelihood a motor nerve can regenerate increases.
A
Doubling the speed at which new nerve cells grow will double the likelihood that a severed motor nerve will reach the muscle it had controlled.
This answer is unsupported. We don’t know if the speed at which nerve cells grow is directly proportional with the likelihood it will reach a muscle.
B
It is sometimes possible, once a nerve sheath has begun to disintegrate, to reverse or slow the process of disintegration.
This answer is unsupported. We don’t know whether it’s possible to reverse or slow the process of disintegration.
C
If a severed motor nerve does not regenerate successfully within three months after being severed, functioning cannot be restored to the muscle that the nerve had controlled.
This answer is unsupported. We don’t know if successful nerve regeneration within three months is necessary for a muscle’s function to be restored.
D
If living nerve tissue could be implanted and sustained within the original sheath of a severed motor nerve, the likelihood that the nerve will regenerate would increase in some cases.
This answer is strongly supported. The only exception to disintegration is if living nerve tissue still exists in the sheath. If living nerve tissue could be injected, then the likelihood of regeneration increases even if only slightly.
E
Without surgical intervention, a muscle that has lost function because of a severed motor nerve is unlikely to regain that function.
This answer is unsupported. We don’t know if surgical intervention is required to restore function to a muscle severed from a motor nerve.
Summarize Argument: Phenomenon-Hypothesis
The author concludes that having a medical self-help book in the home improves family health. This is based on an experiment in which families that were given a medical self-help book experienced a decrease in doctor visits, whereas similar families that weren’t given such a book did not. In addition, we know that improved family health leads to fewer visits to doctors.
Identify and Describe Flaw
The author assumes that having medical self-help books caused a reduction in doctor visits through improving family health. This overlooks the possibility that it may have caused a reduction in doctor visits through some other mechanism. Perhaps, for example, the books didn’t improve health, but simply made families think they don’t need to visit a doctor.
A
it is possible that the families in the experiment who were not given a medical self-help book acquired medical self-help books on their own
This possibility isn’t significant enough to affect how we interpret the study. As long as families that weren’t given a book ended up being less likely on average to own a self-help book than the ones that were given a book, the study’s results can still be evidence of cause.
B
the families in the experiment could have gained access to medical self-help information outside of books
The conclusion concerns the effect of “having a medical self-help book in the home.” Whether the families could access self-help through other means besides a book doesn’t relate to the effect of having a book in the home.
C
a state of affairs could causally contribute to two or more different effects
The flaw doesn’t concern one cause with multiple effects; it’s about one effect (fewer doc. visits) and two dcauses (book, improved family health). Also, if you view the books as causing two effects (improved health, fewer doc. visits), (C) is consistent with the reasoning.
D
two different states of affairs could each causally contribute to the same effect even though neither causally contributes to the other
The author overlooks that two different states of affairs (having book, improved family health) could each contribute to same effect (fewer doc. visits) even though neither contributes to the other. The books didn’t have to cause fewer visits through improving family health.
E
certain states of affairs that lead families to visit the doctor less frequently could also make them more likely to have a medical self-help book in the home
(E) might be true, but in the experiment 500 families were given a self-help book. So we know how these families got the book in their home. We then observed a decrease in doctor visits for these families after they were given a book.
Summarize Argument: Phenomenon-Hypothesis
The author hypothesizes that strokes in the right side of the brain are more likely to go undiagnosed than strokes in the left side of the brain. Why? Because most strokes diagnosed by doctors are left-side strokes.
Notable Assumptions
The author assumes doctors diagnose more left-side strokes because they correctly identify them at a higher rate, and not for any other reason. In particular, this means assuming strokes are no more likely to occur in the left side of the brain than the right.
A
patients who have strokes typically also have other health problems
This is irrelevant. It doesn’t suggest that other health problems make a right-side stroke harder to diagnose than a left-side stroke.
B
it is very likely that just as many strokes occur in the right side of the brain as in the left side
This strengthens the author’s primary assumption: that left-side strokes are no more common than right-side strokes. It casts doubt on the possibility that left-side strokes are diagnosed more often simply because they occur more often.
C
doctors vary greatly in the accuracy of their diagnoses of strokes
This suggests strokes are often poorly diagnosed—but not that right-side strokes are under-diagnosed. It doesn’t say doctors are better at diagnosing left-side strokes than right-side strokes.
D
the symptoms of right-side strokes tend to be different than the symptoms of left-side strokes
This doesn’t say symptoms of left-side strokes are harder to detect than symptoms of right-side strokes. It suggests that left-side and right-side strokes tend to be diagnosed differently, but not that diagnosing right-side strokes is more difficult.
E
other studies have suggested that a large number of minor strokes go undiagnosed
This is irrelevant. It doesn’t say minor strokes are more likely to occur in the right side of the brain, or that left-side minor strokes are more likely to be diagnosed than right-side minor strokes.
Summary
The author concludes that new animated films aimed at adults are not appropriate for children. This is because in order for an animated film to be appropriate for children, it must be innocently whimsical, but not threatening. However, the new animated films for adults have dark themes.
Missing Connection
We know that in order for an animated film to be appropriate for children, it must be innocently whimsical and not threatening. Do we know whether the new animated films are threatening, or whether they lack the quality of innocent whimsy? No; all we know is that the new animated films involve dark themes. To make the argument valid, we want to learn that films involving dark themes are threatening or lack innocent whimsy.
A
Films that are whimsical and mischievous are not threatening.
This doesn’t establish that the new films with dark themes are threatening or that they lack innocent whimsy.
B
Films that are appropriate for adults are seldom appropriate for children.
We don’t know whether the new animated films aimed at adults are appropriate for adults. In addition, even if we did, (B) would establish only that they these kinds of films are rarely appropriate for children. That would not guarantee that they are not appropriate for children.
C
Films that have dark themes are threatening.
(C) establishes that the new films with dark themes are threatening. This establishes that they do not meet one of the necessary conditions for being appropriate for children.
D
Children enjoy films only if the films include animation.
(D) doesn’t establish that the new films with dark themes are threatening or that they lack innocent whimsy.
E
Children do not attend to some details in films aimed at adults.
(E) doesn’t establish that the new films with dark themes are threatening or that they lack innocent whimsy.