问题如下：
The prices of one-period, real default-free government bonds are likely to be most sensitive to changes in:
选项：
A.investors’ inflation expectations.
B.the expected volatility of economic growth.
C.the covariance between investors’ inter-temporal rates of substitution and the expected future prices of the bonds.
解释：
B is correct.
Only changes in default-free real interest rates will affect the price of real, default-free bonds. The average level of default-free real interest rates is positively related to the volatility of economic growth in the economy; thus, changes in the expected volatility of economic growth would likely lead to changes in real default-free real interest rates, which in turn would affect the prices of real, default-free government bonds.
考点：Discount Rate on Real Default-free Bonds
解析：排除法
A， real bonds不会受到通货膨胀的影响，nominal bonds才会。
B，volatility of economic growth影响分母l，即real default-free interest rate，所以B正确
C，one-period的债券价格不受covariance的影响，因为one-period default free bond的covariance=0。只有多期债券才会受covariance影响。
老师，还是有点没太搞清楚：
- 讨论Real Default-free Interest Rate时，当经济向好/增速，Real Default-free Interest Rate会上升，但当增速不确定性增加时，Real Interest Rate会增加。
- 讨论Equity Risk Premium时，当经济向好/增速，又特别强调此时Real Interest Rate会因增速不确定性下降而下降。
我想问：
- Real Default-free Interest Rate ≠ Real Interest Rate ？
- 在做题时，应该怎么去判别应该？
