Q21:

Medicare, the United States government’s health insurance program for the elderly and disabled, covers the full cost of home health care, but not with other nonhospital services where 20 percent of the costs must be paid by beneficiaries.

1. but not with other nonhospital services where 20 percent of the costs must be paid by beneficiaries
2. but not of other nonhospital services, making beneficiaries pay 20 percent of the costs
3. but not of other nonhospital services, for which beneficiaries must pay 20 percent of the costs
4. which is unlike other nonhospital services in that 20 percent of the costs must be paid by beneficiaries
5. which is unlike other nonhospital services that make beneficiaries pay 20 percent of the costs

key:C

偶想问问答案c中for前面的逗号作何用？像这种介词+which 的结构不是紧跟其所修饰名词后面的吗？麻烦各位赐教了~~

这道题关键是理解意思
医疗保障方案（为老年人和残疾人而设立的保险方案）涉及了全额的家庭健康护理，但是没有（covers the full cost）of  其他的非医院护理服务，（这些非医院护理服务）受益人must pay for cost的20%,
for which beneficiaries must pay 20 percent of the costs非限制性定于从句 修饰other nhospital services
如果选C     making beneficiaries pay 20 percent of the costs   就是修饰Medicare了