请各位高手解析一道新GRE逻辑题

题目

请各位高手解析一道新GRE逻辑题
Which of the following most logically completes the argument below?Each year every employee of SAI Corporation must enroll in one of the two health insurance plans offered by SAI.One plan requires a sizable monetary contribution from employees; the other plan is paid for entirely by SAI.Many SAI employees enroll in the plan requiring employee contributions.This fact does not show that they feel that this plan’s benefits are superior to those provided by the plan requiring no employee contribution since----.
　　(A) the plan that requires an employee contribution costs and enrolled employee significantly less per year than do typical health insurance plans offered by corporations other than SAI
(B) only SAI employees who have worked for SAI for at least fifteen years are eligible to enroll in the plan paid for entirely by SAI
　　(C) the two health insurance plans currently offered by SAI are substantially the same plans SAI has offered for the past ten year

答案

人们选择"requiring employee contributions" plan “而不是 “no employee contribution”plan,并不是因为"requiring employee contributions" plan比“no employee contribution”plan 好,而是因为：
所以空里应填第一个 plan不比第二个 plan更好,但人们却又不得不选第一个的原因.B选项说了,是因为不到十五年的工作时间,人们即使想选第二个plan也选不了.这个符合逻辑,所以可以选.
C说两个plans 和十年前没啥变化体现不出人们为啥要选不好的第一个plan