单选题 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.

【正确答案】 B
【答案解析】[解析] 一系列有相同执行价和不同到期日的利率看跌期权构成的是利率底(interest rate floor)，而一系列利率看涨期权可被看作利率顶(interest rate cap)。