A. strengthens the conclusion

B. prior job performance is out of scope

C. rationale for hiring Roger is out of scope

D. explains an alternative cause for the poor sales performance=> Roger not responsible=>weakens the conlusion that Roger should be fired

E. Roger might have scored high in a test, but the fact remains that the actual sales peformance of the company suffered. doesnt affect the conclusion

hence D

B, C and E are easy to eliminate. I got confused between A and D. My interpretations:
A: The option shows that any new manager takes some time to adjust. During this transition phase, some intial reduction in sales is expected. Hence, if company fires Roger and hires a new manager then sales might drop further. Therefore, company should not fire Roger. This weakens the conclusion.

D: This option is straight. Overall auto market condition itself is grim, so is the company's sale.

Although I selected D, I didn't find D having any clear merit over A. Looks like I have assumed too much in A; is that the case?

thanx scoobydooby and karmyogi. I was also confused between two choices, A and D. I went for A. but how can A strengthen the conclusion as said by scoobydooby? OA is D. In case of options like D should we assume that the demand for every company has decreased?

@vertigo05

While I was reading the question, I arrived to the conclusion even before reading the options.

Actually here the conclusion is to fire Roger, why??
Because he is not able to increase sales, rather the sales decreased after he was hired.

Now we have been given a fact that the sales decreased,But if we are able to find an alternate explanation to the decrease in the sales,so we can prove the Roger was fine with his job!

D provides that alternate explanation

I will go with D