First things first: what's our core?
Conclusion:
the explanations do not justify the invasions of privacy
Premise:
the explanations are self-serving
Now, before we go to the choices, let's consider what gaps or flaws might exist here. There is a pretty clear connection required for the argument to work, namely the connection between the explanations being self-serving and the explanations not justifying the behavior. We might picture this in our minds like this: self-serving --> don't justify.
So what's wrong with that? Well, just because an explanation is self-serving, does that automatically make that explanation bad? Not quite. With this anticipation in mind, let's head to the choices.
(A) this doesn't happen here.
(B) the author does not assume this.
(C) "far higher"? nah, the argument doesn't do that.
(D) motives? Is that what "self-serving" means? Maybe. Let's leave it.
(E) no, this is not a generalization argument.
Therefore, D is our answer! This is exactly what the argument does -- it says that the employer's explanations are no good because of the employers motivation to "self-serve."