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。
为什么growth volatility越大，l越大呢？是讲义中哪句话？
我理解的讲义中只是说未来growth预期越大，l越大，但是growth越大和growth volatitlity越大是两码事。。
