问题如下：
At the time of purchase, Jacques used CAPM to estimate a required return for PZ by incorporating an unadjusted historical equity risk premium estimate for the US equity market. However, the US equity market has experienced a meaningful string of favorable inflation and productivity surprises for past several years. In order to mitigate that concern, the historical equity risk premium Jacques used as an estimate of the forward-looking equity risk premium should be:
选项：
A.adjusted upward
B.adjusted downward
C.left unchanged
解释：
B is correct.
考点：Equity risk premium
解析：B是正确的。一系列有利的通胀和经济增长的惊喜可能会带来一系列高回报，从而提高股票风险溢价的历史平均估值。为了计算得到合理的要求回报率，分析师应下调历史的股票风险溢价。
请问思路是不是使用CAPM公式？因为市场预期较好、未调整，所以RM-Rf偏高，导致Re偏高，所以要向下调低？
