— How often do you eat out? 

— _____, but usually once a week. [ ]

A. It depends

B. Have no idea

C. As usual

D. Generally speaking

爱莉诺•奥斯特罗姆把制度分为以下几个层次（）

A、宪法选择

B、集体选择

C、法律选择

D、操作选择