The conclusion of this argument is that the company treats its employees fairly. Why? Because those retirees who responded to a survey said they had been treated fairly.
The issue I see, and that (D) hinges upon, is that we don't know about the folks that didn't respond. What if triple the number of people didn't respond? And, it's possible that people who responded tended to be happier with the company.
(A) is referring to circular reasoning, but this argument uses a survey to draw a conclusion. Not circular!
(B) is silly - why can't the survey be verified?
(C) makes me say "hunh?" Fairly means fairly in this argument.
(E) is perhaps tempting if you thought the issue was that the survey was of retirees, and maybe now the company treats employees differently, however, there's no assumption that the old ways are better than the new - the assumption is basically the opposite - that the old ways can tell us about what's going on now.
There are some other gaps in this argument - specifically, does a survey of retirees speak to current conditions? - however you pointed out some issues that are not germane to the argument:
The fact that the survey is recent is irrelevant. The conclusion is about current conditions.
Also, "good relations" is part of the background of the argument, not the core. The argument isn't trying to prove that the company is proud of its long history of good relations with its employees. The argument is about what can be concluded based on the survey.
#officialexplanation