C is the only choice that offers a valid criticism of the plans actually laid out in this paragraph. The remaining employees are "already working at capacity", meaning that there's no slack in their schedules. So, if they're roped into attending a mandatory training session, that time will have to come at the expense of actual productivity.
.
Wrong answers:
A/ Addressing factors that led to the loss of people
who are already gone (= "more flexible work schedule policies", according to the opening sentence) wouldn't bring those people back—and wouldn't meaningfully speak to anybody who's still there, since the remaining people are the ones who DIDN'T consider those things important enough to quit and go work for the employer that offers them.
B/ D/ E/ There's nothing here to suggest that anybody had any of these things in mind. (GMAC will not give you three choices that all read similarly and are all wrong for exactly the same reason.)
You can also eliminate all three of these because the question asks you to find a criticism of the
concrete ACTIONS that are explicitly suggested... which means exactly what it says. ACTIONS don't "make assumptions", so there's no reason to read any of these choices past the second word.
.
BTW sloppy wording in this one. "At capacity" should mean what it says, which is that these employees
cannot possibly take on any more work. ("Capacity" means absolute maximum possible throughput. Working "over capacity" is impossible.) But if the employees really ARE already working
at 100% of capacity, then the company is making impossible demands of them.
The GMAT will not present arguments with impossible goals or self-contradictory logic..