请教一个一个GMAT逻辑思路-是否因果对结果否就错呢？

三塘木

20. A rise in the percentage of all 18-year-olds who were recruited by the armed services of a small republic between 1980 and 1986 correlates with a rise in the percentage of young people who dropped out of high school in that republic. Since 18-year-olds in the republic are generally either high school graduates or high school dropouts, the correlation leads to the conclusion that the republic’s recruitment rates for 18-year-olds depend substantially on recruitment rates for high school dropouts.

Which one of the following statements, if true, most weakens the argument?
(A) A large number of 18-year-old high school graduates were recruited for the republic’s armed services in 1986 than in 1980.
(B) Many of the high-technology systems used by the republic’s armed services can be operated only by individuals who have completed a high school education.
(C) Between 1980 and 1986 the percentage of high school graduates among 18-year-olds recruited in the republic rose sharply.
(D) Personnel of the republic’s armed services are strongly encouraged to finish their high school education.
(E) The proportion of recruits who had completed at least two years of college education was greater in 1986 than in 1980.

再来看题目，用helr的方法来做的话：
１ 找结论和前提：
结论：
republic’s recruitment rates for 18-year-olds depend substantially on recruitment rates for high school dropouts
前提：
A rise in the percentage of all 18-year-olds who were recruited by the armed services of a small republic between 1980 and 1986 correlates with a rise in the percentage of young people who dropped out of high school in that republic

２ 看推理模式：我们可以看出来，原题作者把参军率和退学率两个不相关的事情放在一起，时间发生的一致，然后发现了两个有正相关关系，所以推断出参军率和退学率相关。这个很明显是相关因果类的题。相关因果的题是和因果果因完全不同的，相关因果是涉及到了两个变量（这里一个自变量Ｘ退学率一个因变量Ｙ参军率），然后判断说两者在pattern上有正相关，所以推测出ＸＹ是相关的。
针对相关因果类，ＣＱ有四个，因果相关性不存在，第三因素，中间因素和因果方向问题。在这道题的选项里，只有Ｃ是直接攻击了因果相关性的问题，证明说高中毕业的学生参军率也有急速上升，并不是说一定是退学率的上升导致的参军率上升。
希望这个能有帮助