问题如下图：
选项：
A. 
B. 
C. 
解释：
为什么要引入边际替代率这个概念？边际替代率越低实际利率越高？即边际替代率越低代表不耐情绪越高？然后不耐情绪越高所以需要补偿的实际利率就越高？
NO.PZ2015121810000029 解析是 investors are less worrieabout the future antheir consumption abilities in the future—this, their inter-temporrate of substitution is low 不过我记得m = U未来/U现在 只能通过这个逻辑链条来理解吗未来好，未来更有钱，财富增加会导致U较小，所以U未来减小，而U现在不变，所以m减小？
NO.PZ2015121810000029 A，borrowing 增加，不应该是推动价格上升，利率降低吗？而且应该是borrowing减少吧，经济好的时候，大家把钱都拿去消费了，所以borrowing投资减少，所以利率上升，刺激投资。不知道这样理解对不对？
have high inter-temporrates of substitution. have high uncertainty about levels of future consumption. A is correct. The average level of fault-free reinterest rates is positively relateto the expecterate of growth of the unrlying economy analso to the volatility of economic growth in the economy. ring perio of high expecteeconomic growth, investors are less worrieabout the future antheir consumption abilities in the future—this, their inter-temporrate of substitution is low, so they borrow more toy ansave less. Other things being equal, this means ththe average level of fault-free reinterest rates (the reciprocof the rate of substitution, see Equation 4) shoulhigher in economy with high growth, anlower in economy with lower, more stable growth. 考点Refault-free interest rates 解析 economic growth增加，投资者的收入会增加，不担心未来没钱，所以储蓄减少，增加消费，所以信贷消费也会增加， current borrowing增加， A正确。current borrowing增加推动利率上涨，所以 fault-free reinterest rates 较高。 B，结论经济增速变快，m减小。因为m=MUt+s/MUt, 经济变好，将来收入增加，投资者更有钱了，所以将来消费的爽度减小，MUt+s减小，所以m减小。 C，经济好的时候，将来消费的不确定是比较低的。因为经济好，投资者不担心将来没钱，所以会减少储蓄，增加消费，因此将来消费的不确定性低。没有在讲义里找到关于current borrowings 增加的内容啊
是不是题干没有这句话countries with high expecteeconomic growth。 那么C就对了，因为volatility of future consumption = volatility G, G波动越大则fault free rate 大，是正向关系
这个reang的理论都是用跨期替代率或者说资金供给来各自利率，从未引进资金需求这一概念，如果要用传统经济学的资金供求理论来利率，那么完全是另一种框架，甚至和本reang的理论是冲突的，这里出现A实在太牵强了。
