Answer choice (D) is tempting, huh? It's probably the most tempting of the incorrect answers. It's tempting for a reason too, and the test-writers use this a ton to make tempting answer choices on Strengthen questions.
Answer choice (D) supports a premise, but that can't be used to "strengthen the reasoning." We already assume the premises are true. We want to support the conclusion reached on those premises.
The argument says that because layoffs damage morale less than reducing wages, companies are likely to reduce personnel costs through layoffs. Answer choice (A) is nice in that it makes the evidence relavent by saying that it's the primary concern. It's not tough to see this as supporting the conclusion and that probably wasn't something the LSAT writer was trying to conceal. It was more about forcing you to decide between (A) and (D), waste time, and rattle you a bit since you wouldn't be certain by the time you had to move on.
(B) is out of scope since increasing wages is not up for discussion.
(C) is out of scope. Profits are not being discussed.
(D) is tempting and supports the evidence (Premise Booster), but not the argument's reasoning.
(E) would weaken the argument that layoffs would be the best way to go for companies.
Does that answer your question?
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