Yes, Choice D is the answer. Here is my explanation.
Analysis :- Hallmarks' margins are decreasing. Executive asserts that by increasing productivity hallmark would be able to restore the margin. He concludes that by reducing the workforce by 10 to 20% hallmark can increase the productivity (This is what we have to weaken) as well as the remaining workforce would get incentive to work in additional hours.
Any answer choice that states against the
reduction in workforce - increase in productivity relationship would weaken the conclusion substantially.
A) Incorrect. We are discussing productivity as a whole and not that of base or additional hours. It may also be true that by achieving maximum productivity in base hours the hallmark might restore its margins.
B) hallmarks' margins are hampered and sales perhaps not. In Nov-Feb hallmark might will do the maximum sale but whether its margins would get restored by that sale? Not known. So incorrect.
C) again the same false relationship
increased sales - increased margin.D) Correct. directly breaks
reduction in workforce - increase in productivity relationship.
E) This choice only suggests the alternate way to increase profits, but does not argue against the way mentioned in passage.