Its an easy A).
The key in such convoluted questions is to not get intimidated by the language - instead try to work out the logic used. G.B.Shaw [great character btw

] made the argument criticizing the causal argument made by the nation's Govt.
The nation's govt realized that if bakers have a monetary incentive of profiteering in baking bread, the nation would be well fed. G.B.Shaw criticizes this causal logic and extrapolates it in the case of surgeons who could be given a monetary incentive for cutting legs [
red flag: extreme logic used, possible clue for answer]. He obviously fears that surgeons would go around cutting legs even in the cases that don't require this.
The Question asked is "Shaw's statement would best serve as an illustration in an argument criticizing which of the following?
Now proceed to the options:
A) Says some dentists would do unnecessary dental work if given a profit incentive.
This is most parallel to "surgeons who cut legs in cases that are not required. "
B) C) D) E) talk about OT or distortions like "raising mkt share", "increasing the profit margin (as opposed to creating one in the first place) " etc. etc.