GENERAL METHOD:

In CR, Strengthen and Assumption are always considered the most difficult questions. To solve Strengthen question, we should:
- Identify the conclusion - This is what you're trying to strengthen. MOST important.
- Personalize the argument if you can.
- Look for weaknesses in the argument - It seems contradict, but in real GMAT, the answers are always used to eliminate that weakness. Frankly, that's the logic GMAC uses

APPLY:

Premise: Generic drugs contain exactly the same active ingredients as their brand name counterparts, but usually cost much less
Conclusion: generic drugs are just as effective as their brand-name counterparts, but cost considerably less

What is the weakness: having same ingredients does not mean having same quality - KEY Point.
Best answer will eliminate that weakness.

Let consider each answers:

(A) The ingredients used in the manufacture of brand name drugs cost no more than the ingredients used to produce their generic counterparts. - WRONG - Shell game - it just talks about the cost of ingredients, but it doesn't say generic drugs have same quality as brand name drugs. There's possibility that brand name drugs quality is much better than generic drugs quality, that's why brand name drugs are sold at higher price.

(B) Generic drugs are just as likely as brand-name drugs to be readily available in pharmacies. - WRONG - OUT of scope- the question says nothing about the availability.

(C) Generic drugs are no more likely than brand-name drugs to suffer from defects in composition. - CORRECT - it says generic drugs do not have more defectiveness than brand name counterparts. It means the two drugs maybe have same quality, but generic costs much less.

(D) The higher cost of brand-name drugs underwrite drug companies' heavy investment in research. - WRONG - Out of scope. Nothing about investment in research.

(E) Because of advertising, doctors frequently prescribe brand-name drugs by their brand-name, rather than by their chemical name. - WRONG - Out of scope.


Hope it helps.

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