请问什么是ask price 什么是bid price

等权重市场指数的计算逻辑请再解释一遍，以及如何调整股票权重

新的difference为什么是加上150000？difference怎么算？

A怎么理解？

为什么A公司杠杆增加导致AB两公司的ROE差值近似？C选项的逻辑在哪里？

连续支付、支持层级，计划摊还类别层级，这3个关系时候啥，有图列式么？

为啥不选B？

The single monthly mortality ，这里的mortality 翻译成啥？

这题中A为什么是错的？

Suppose the prospects for recovering principal for a defaulted bond issue depend on which of two economic scenarios prevails. Scenario 1 has probability 0.75 and will result in recovery of $0.90 per $1 principal value with probability 0.45, orin recovery of $0.80 per $1 principal value with probability 0.55. Scenario 2 has probability 0.25 and will result in recovery of $0.50 per $1 principal value with probability 0.85, or in recovery of $0.40 per $1 principal value with probability 0.15. A. Compute the probability of each of the four possible recovery amounts: $0.90, $0.80, $0.50, and $0.40. B. Compute the expected recovery, given the first scenario. C. Compute the expected recovery, given the second scenario. D. Compute the expected recovery. E. Graph the information in a probability tree diagram. 图为我做题的过程，B、C、D这三问题，算出来的结果跟答案不一样？我到底错在哪个地方？