单老师讲的价格弹性用ed来表示，但是课件中都是用的Ep，那价格弹性的表示到底是ed还是Ep？

根据公式，价格弹性是否恒为负数？那这里为什么还能跟1进行比较？是取绝对值之后的比较吗？那提及价格弹性到底是原始的负数还是取绝对值之后的数？

B选项怎么理解？

衰退最底部，应该是劳动生产率最低吧。因为随着衰退的进行，企业渐渐降低了劳动生产率，在底部时劳动生产率最低

A的roll yield是什么意思

为什么说MP=AP时，AP最大？过程如何推导？

老师，请问Fixed charge coverage中的 分子的lease payment是作为lessee的OL还是lessor的OL，那分母的lease payment是作为essee的OL还是lessor的OL？麻烦老师解读一下。谢谢

A mutual fund manager wants to create a fund based on a high-grade corporate bond index. She first distinguishes between utility bonds and industrial bonds; she then, for each segment, defines maturity intervals of less than 5 years, 5 to 10 years, and greater than 10 years. For each segment and maturity level, she classifies the bonds as callable or noncallable. She then randomly selects bonds from each of the subpopulations she has created. For the manager’s sample, which of the following best describes the sampling approach? A Stratified random. B Simple random. C Systematic. 上一题  正确答案A 您的答案B 本题平均正确率：92% Sampling, time-series and cross-sectional data难度：一般 推荐：      答案解析 In stratified random sampling, one divides the population into subpopulations and randomly samples from within the subpopulations. 请问： 1.分层是一定要求每组中有固定比例吗？ 2.系统抽样是每组中第Kth个的那种吗？

kinked model中MR为什么会有缺口？

弹性为1时，revenue最大。为什么？