请各位高手解析一道新GRE逻辑题

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 years
　　(D) most of the SAI employees enrolled in the plan paid for entirely by SAI are under 50 years old
　　(E) both plans offered by SAI provide benefits not only for employees of SAI but also for children and spouses of enrolled employees为何不选C选B?请赐教!
懂了懂了!原来我只纠结在最后一句而忽略了上下文!受益匪浅!