Between c and d

The strategy used is that the general principle given, i.e. people should be rewarded for doing a given job in proportion to the effort it costs them to do it, is undermined by showing that this principle leads to undesirable consequences, i.e. it would mean that those people with the least skill or natural aptitude for a particular task would be the ones given the most incentive to do it. Therefore, (C) is wrong because the argument does not show that a consequence need not follow from a principle, rather it shows that a consequence does indeed follow form the principle, and therefore we should no follow the principle. Hope that clears things up! Please let us know if you have any other questions.

The test told me that D was wrong and C was right. but your saying D is right and C was wrong.

My book also tells me that C is the correct answer^