According to some sports historians, professional tennis players develop unique playing styles that result from a combination of the peculiarities of each player's physical attributes and the influence of coaches during their early adaptation to the game. But when the increase in strength and endurance of modern players is discounted, it becomes readily apparent that the playing styles of the current crop of professional tennis players are no different from the styles of players from previous generations. Clearly, there is a universally efficient tennis style to which all professional tennis players conform.
The argument above is most weakened by which of the following statements?
All of the early coaches of today's professional tennis players were professional tennis players themselves earlier in their lives.
The author begins by describing the view of some sports historians, who subscribe to a basic formula: physical attributes + a coach's influence = a player's "unique” tennis style. After dismissing the relevance of modern payers' greater strength and endurance, however, the author argues that current styles are really no different from previous styles, implying that the historians' claim of the existence of "unique” tennis style is bogus. And this implication is stated outright in the last sentence, where the author posits the existence of a universally successful tennis style shared by all professionals. In other words, the author uses the fact that tennis styles haven't changed over the years to argue that there's simply one best way to play tennis: in contrast to that historians' theory of "unique”, the author proposes the theory of "universality”. But the author ignores a possible alternative explanation: namely, the role of the tennis coach. If as (D) has it, the early coaches of today's players were the professionals of yesteryear, then it's reasonable to believe that the style the author considers "universal” may simply be the style (one possible one among many) that was handed down from one generation to the next. Perhaps if the current crop of tennis stars doesn't go on to teach the next generation, whole new styles will develop. If the current style is learned, then it may not be universally inherent to the game. If (D) is true, the author's claim of "universality” is weakened. That makes (D) the best answer choice.
(A) emphasizes the truth of the first part of the sports historians' view regarding the individuality of physical attributes. Since the author doesn't explicitly disagree that players vary in terms of some attributes, this choice doesn't weaken the argument.
(B) If anything, strengthens the argument: if most current players don't know of the players of previous generations, yet their styles are for the most part similar to that of those players, then we'd be more likely to believe that the author is on to something with the claim that a universally efficient style exists in the world of professional tennis.
(C) makes an irrelevant distinction between strength and endurance. Saying that one has a greater impact than the other has no effect on the argument, which never can begin to rank those two factors.