64. Unlike a funded pension system, in Which contributions are invested to pay future beneficiaries, a pay-as-you-go approach is the foundation of Social
Security.
(A)a pay-as-you-go approach is the foundation of Social Security
(B) the foundation of Social Security is a pay-as-you-go approach
(c) the approach of Social Security is pay-as-you-go
（D）Security's approach is pay-as-you-go
（E）Social Security is founded on a pay-as-you-go
approach
知道是考与pension system对应的一个词，但是觉得social security也不是很对应啊，这应该是社会保障部门吧，怎么能算一个system呢？ 哪位NN能帮忙解释一下么？谢谢
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