【题目】That raised the costs of Medicare, ______ represented 15% of the federal funds last year.
A.it
B.what
C.which
D.that

【答案】C
【解析】句意：这增加了医疗保险的成本，这代表去年联邦基金的15%。此句构造了了非限制性定语从句，用which指代前面的句子，在定语从句中作主语。故选C。