They are not assuming that diet is the only relevant factor. However, it is essentially right to say that it is the only thing being discussed. So, C is somewhat relevant but it doesnt really do anything to the argument.
1. Must strengthen the argument (fails this test)
2. Negation of the answer choice destroys the argument as a whole
I doubt this would meet the standard of instructors logic but at least you'll somewhat get a sense of why C isnt the right answer
VictoriaApril 23, 2019
Hi @nybard,
Roland's argument concludes that modifying our diet is not worthwhile. They cite two reasons which support this conclusion.
Firstly, Roland says that, if everyone follows Myrna's recommendation for their entire life, then only 0.2% of people would lengthen their lives by an average of 3 months.
Secondly, Roland says that following this diet recommended by Myrna is a sacrifice as low-fat diets are unappealing. They say that this sacrifice is too much to ask as the reward for doing so is, on average, an additional three months of sacrifice.
As suggested by @Maybeillgetlucky, we are looking for the answer choice that, if negated, destroys the argument, i.e. no longer allows the conclusion to be logically drawn.
Therefore, we are looking for an answer choice that, if negated, conflicts with either the statement that only 0.2% of people would lengthen their lives by an average of three months OR that the sacrifice of an unappealing diet that is required is too much to ask for only three more months of that sacrifice as a reward.
A) Roland is arguing that, in this case, it is not desirable to live in such a way as to lengthen life as much as possible. Therefore, this answer choice negated actually supports Roland's argument.
C) This statement is irrelevant to Roland's overall argument. Even if there are more factors than diet to consider when computing influences on length of life, Roland and Myrna are arguing about whether people should follow low-fat diets or not. Therefore, other factors that affect length of life are not relevant to this discussion.
D) As with answer choice A, this answer choice negated actually supports Roland's argument.
E) Again, this is irrelevant to Roland's argument. It does not matter how many people eat the average diet as this neither supports nor refutes Roland's conclusion nor the pieces of evidence they present.
B) This is the correct answer as, if negated, it directly conflicts with Roland's second piece of evidence. If a low-fat diet can readily be made appealing and satisfying to a person who follows it regularly, then there is no sacrifice to be made. If there is no sacrifice to be made, then following a low-fat diet would extend 0.2% of peoples' lives by an average of 3 months with no cost. This no longer allows Roland to logically draw their conclusion that modifying our diet is not worthwhile.
Hope this is helpful! Let us know if you have any further questions.
