Dentist: I recommend brushing one’s teeth after every meal to remove sugars that facilitate the growth of certain bacteria; these bacteria produce acid that dissolves minerals in tooth enamel, resulting in cavities. And when brushing is not practical, I recommend chewing gum—even gum that contains sugar—to prevent the formation of cavities.
"Surprising" Phenomenon
Why would chewing sugary gum after a meal help to prevent cavities when sugar is known to lead to the formation of cavities?
Objective
The right answer will be a hypothesis that explains why chewing gum after a meal helps to prevent the formation of cavities. That explanation must offer some dental hygiene benefit of chewing gum that has the potential to outweigh any damage that could be caused by the sugar in some gums.
A
A piece of chewing gum that contains sugar contains far less sugar than does the average meal.
We would expect this to be true—think of how small a piece of gum is! This answer doesn’t explain why chewing gum helps to prevent cavities, though, so it doesn’t reconcile the paradox in the stimulus.
B
Tooth decay can be stopped and reversed if it is caught before a cavity develops.
While this might be relieving to hear on a personal level, it doesn’t help to reconcile the paradox at hand. We need information about how chewing gum after meals helps to prevent cavities, and this answer choice doesn’t give us that.
C
Chewing gum stimulates the production of saliva, which reduces acidity in the mouth and helps remineralize tooth enamel.
This is helpful! Sugar leads to cavities because it causes enamel to dissolve, but chewing gum protects enamel. It makes sense, then, that chewing gum after meals helps to prevent cavities even if the gum contains some sugar.
D
Sugars can be on teeth for as long as 24 hours before the teeth-damaging bacteria whose growth they facilitate begin to proliferate.
This answer choice has nothing to do with the cavity-prevention benefits of chewing gum after meals, which is what we need the answer to explain!
E
Chewing gum exercises and relaxes the jaw muscles and so contributes to the overall health of the oral tract.
This answer doesn’t help because it has nothing to do with the impact that chewing gum has on cavity formation. The “overall health of the oral tract” could refer to factors other than cavities.
A
The unearthed land mammal is only one of several ancient land mammals that were indigenous to New Zealand.
B
The recently discovered land mammal became extinct long before the native bird population was established.
C
The site at which the primitive land mammal was unearthed also contains the fossils of primitive reptile and insect species.
D
Countries with rich and varied native land mammal populations do not have rich and varied native bird populations.
E
Some other island countries that are believed to have no native land mammals in fact had indigenous land mammals at one time.
A
The newspaper reporter who panned the restaurant acknowledges having no special expertise about food and its preparation.
B
The previous job of the newspaper reporter who panned the restaurant was as a political reporter.
C
The newspaper reporter who panned the restaurant is a good writer.
D
The newspaper reporter who panned the restaurant is not a true restaurant critic.
E
A newspaper would never call someone a drama critic who had no special training in theater.
Library preservationist: Due to the continual physical deterioration of the medieval manuscripts in our library’s collection, we have decided to restore most of our medieval manuscripts that are of widely acknowledged cultural significance, though this means that some medieval manuscripts whose authenticity is suspect will be restored. However, only manuscripts whose safety can be ensured during the restoration process will be restored, and manuscripts that are not frequently consulted by researchers will not be restored.
Summary
Most of our medieval manuscripts that are of widely acknowledged cultural significance will be restored, and some medieval manuscripts whose authenticity is suspect will be restored. Only manuscripts whose safety can be ensured during restoration and manuscripts frequently consulted by researchers will be restored.
Notable Valid Inferences
Some medieval manuscipts whose authenticity is suspect are frequently consulted by researchers.
Some medieval manuscripts whose authenticity is suspect can have their safety ensured during restoration.
Most medieval manuscripts that are of widely acknowledged cultural significance are frequently consulted by researchers.
A
Some of the medieval manuscripts whose authenticity is suspect are frequently consulted by researchers.
Must be true. As shown below, we can combine the statements that some manuscripts whose authenticity is suspect will be restored and that only frequently consulted manuscripts will be restored. 
B
All of the medieval manuscripts widely acknowledged to be of cultural significance are manuscripts whose safety can be ensured during the restoration process.
Could be false. The stimulus tells us that most manuscripts widely acknowledged to be of cultural significance will be restored. We cannot infer an “all” statement from a “most” statement.
C
All of the medieval manuscripts whose safety can be ensured during the restoration process are frequently consulted by researchers.
Could be false. As shown on our diagram, there are no necessary conditions attached to the condition of a manuscript’s safety being ensured. It is possible that some manuscripts exist whose safety can be ensured but are not frequently consulted.
D
The medieval manuscripts most susceptible to deterioration are those most frequently consulted by researchers.
Could be false. The stimulus does not give us any information to determine what manuscripts are most susceptible to deterioration. This answer choice is outside of the scope of our conditions.
E
None of the medieval manuscripts that are rarely consulted by researchers is widely acknowledged to be of cultural significance.
Could be false. The stimulus does not give us any information about manuscripts that are rarely consulted by researchers. This answer choice is outside of the scope of our conditions.