Self-study
Cafeteria patron: Support The apples sold in this cafeteria are greasy. ███ ███████ ████ ██ ████ ███ ██████ ███ ██ ████ █████████ ████ ████ ███ █████████ ██ ███ █████████ ███ ████ ███ █████████ ████ ███ ████ ███ ██████ ██ ██████ ████ █████ ██ ███████ ████ █████████ ██████████ ██████ ██ ██ ██████████ ███ ██ █████████ █████ ██ ██ ███████ ████████ ███ █████████ ██ ███████ █████████████████ ██████ ███████ ███████████ ███ ████████
Argument Breakdown
The patron concludes that a cafeteria is endangering patrons by selling fruit covered with pesticides. This is supported using the specific case of the apples sold by the cafeteria. These apples have a greasy residue, which is present when they're delivered to the cafeteria. Furthermore, the cafeteria doesn't wash the apples before selling them. And finally, a majority of fruit is treated with pesticides, and remains dangerous until being washed.
The patron uses two strategies to suggest the cafeteria's apples are dangerous. One is the statistical argument that most fruits are pesticide-treated, and so probably these apples are too. The second is the specific detail that the apples are greasy, which the patron seems to think is linked to pesticides.
Objective: Identify a Necessary Assumption
Despite the evidence given, the patron doesn't actually establish that the apples are pesticide-treated. That makes it necessary to assume that this is the case. But keep in mind, it's not necessary to assume the grease is from pesticides. Even if the grease was unrelated, the apples could still be pesticide-treated. There are other ways to get there, making the grease unnecessary.
The other necessary assumption we can spot is that the apples aren't washed before being delivered to the cafeteria. Even if they were pesticide-treated, and although the cafeteria doesn't wash them, they would still be safe if they were washed right after being harvested.
And of course, it's always possible there's another necessary assumption that we didn't spot. If necessary, we can fall back on our negation and must-be-true tests to search out the correct answer.
10.
Which one of the following ██ ██ ██████████ ██ █████ ███ ████████ ████████
a
The apples that ███ █████████ █████ ███ ███ ██████████ ██████ █████ ███████ ███ ██████ ████████ ███ ██████████
In other words, since we know the cafeteria doesn't wash the apples, they aren't washed at all. Regardless of how many pesticides are used before harvest, the apples would be safe if they were washed. That makes it necessary to assume they're not washed before they reach the cafeteria—if they were, there would be no issue.
b
Most pesticides that ███ ███████ ██ █████ ██████ ███████ █████ █ ██████ ███████ ██ ███ ██████
(B) has two problems. First, it's not necessary for the grease to be pesticide-related. The apples could be greasy for a totally different reason, and that wouldn't harm the argument as long as they were also pesticide-treated.
Second, "most" isn't enough to say that these specific apples are greasy from pesticides. (B) wouldn't eliminate the possibility that the apples were never pesticide-treated, and just got greasy some other way.
c
Many of the █████████████ ███████ ███ ███████ ████ ███ █████████ ████ ███ ████ ███ ██████ ██ ██████
The argument isn't concerned with patrons' awareness, but with the actual danger posed to them by these apples. No assumption about patrons' mental state is necessary to the argument.
d
Only pesticides that █████ █ ██████ ███████ ██ █████ ███ ██ ██████ ████
The argument doesn't distinguish between types of pesticides—it doesn't even establish a link between pesticides and greasiness. Which pesticides are or aren't washable doesn't make any difference to the argument.
e
Fruits other than ██████ ████ ██████ ██ ███ █████████ ██ █ ██████ ██████████
Even if we knew for sure that greasiness was related to pesticides, (E) wouldn't be necessary. If the apples are the only problematic fruit the cafeteria sells, that's still enough for the conclusion that the cafeteria is endangering patrons.