Answer: D.". . . when well trained, no children are more courteous and agreeable," because courteousness and agreeableness are not traits that can be statistically measured.
This is the sentence that uses fallacious reasoning. It argues that when American children are well-raised, they are the kindest and most courteous of all children. This statement is a fallacy, because there is no way to know if American children are really the most agreeable of all nationalities. This is something that cannot be properly measured.