Conclusion: A growing number of people who are seeking a healthier way to live are turning to vegetarianism
Premise: The average person who switches to a vegetarian diet will lose fifteen pounds in a year. Anyone aware of this fact will surely choose vegetarianism over any other diet.

Option C and D come close

C is correct

option D explains: For some people are fifteen pounds is still not a sufficient amount of weight to lose---> which does not impact much to conclusion

Diet it is not the same as healthier way, it is an option to lose weight.
Option D is correct

Between C and D, C is the clear winner. It is because D says that 15 pounds loss of weight is still not enough. Ok. But that doesn't challenge the idea of vegetarianism. 15 pounds is not enough but still is something.

On the other hand C clearly weakens the argument by stating that people who choose healthy way of life are not concerned with weight loss. So, people aware of the fact will not always opt for vegetarianism.

Thus, I find C best.

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IMO B. The conclusion is that those aware of the fact that those who become vegetarians lost 15lbs on average per year will choose to become vegetarians but choice B challenges this by saying exercise is not taken into account. What if it were the exercise, and not the diet that led to the weight loss? I think this is the missing assumption and choice B would therefore weaken the conclusion.

Question Explanation:

Conclusion: Anyone aware of this fact will surely choose vegetarianism over any other diet.

Premises: A growing number of people who are seeking a healthier way to live are turning to vegetarianism. The average person who switches to a vegetarian diet will lose fifteen pounds in a year.

Assumption: Anyone seeking a healthier way to live wishes to lose weight.

The question stem asks to challenge the conclusion, so this is a weaken question. The passage states that the average person who switches to a vegetarian diet will lose fifteen pounds in a year. Based on this weight loss, the passage concludes that anyone aware of this fact will surely choose vegetarianism over any other diet. In order to support the claim that anyone aware of the weight-losing effects of vegetarianism will surely choose such a diet, the passage must assume that all people seeking a healthier way to live wish to lose weight. As this is a weaken question, the correct answer will attack this assumption. Evaluate the answer choices.

Choice A: No. How expensive the diet may be is out of scope. The correct answer must weaken the assumption that anyone seeking a healthier way to live wishes to lose weight. The cost of vegetarianism or any other diet is not relevant.

Choice B: No. Weight loss due to exercise is out of scope. The argument is concerned with the weight loss effects of a vegetarian diet, not that of any of the other ways to lose weight.

Choice C: Correct. According to this answer choice, a person seeking a healthier way to live could be aware of the weight-losing effects of vegetarianism, yet choose not to adopt such a diet because that person is not concerned...with weight loss.

Choice D: No. Sufficient amount of weight is out of scope. The argument relies on the universal desire to lose weight, not whether a certain amount of weight loss is sufficient for everyone.

Choice E: No. This choice is out of scope. The passage is concerned with the weight-losing effects of a vegetarian diet, not small amounts of fish or whatever else a person may choose to eat.

The correct answer is choice C.
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