创新是一个民族发展的灵魂，中 * * 自古以来就作出了不少的创造发明，其中唐朝时期创制的农业生产工具是[ ]

A、耧车    

B、翻车    

C、水排    

D、曲辕犁

An analyst does research about options. A series of interest rate call options expiring on different dates but having the same exercise rate is best characterized as a(n):

A. zero-cost collar.
B. interest rate cap.
C. interest rate floor.