When I try to understand ______ that prevents so many Americans from being as happy as one might expect, it seems to me that there are two causes.

A．why it does

B．what it does

C．what it is

D．why it is

医疗保险费用支付中属于被保险方的支付方式是（）。

A.按住院日定额付费方式

B.按服务项目付费方式

C.最低起付标准方式、按比例分担方式、最高保险限额方式、混合方式

D.按病种付费（DRGS支付体系）方式

E.按人头付费