问题如下：
8. All else being equal, if the shape of the yield curve changes from upward sloping to flattening, the value of the option embedded in Bond #2 will most likely:
选项：
A. decrease.
B. remain unchanged.
C. increase.
解释：
C is correct.
Bond #2 is a callable bond, and the value of the embedded call option increases as the yield curve flattens. When the yield curve is upward sloping, the one-period forward rates on the interest rate tree are high and opportunities for the issuer to call the bond are fewer. When the yield curve flattens or inverts, many nodes on the tree have lower forward rates, which increases the opportunities to call and, thus, the value of the embedded call option.
我是这样考虑的：yield curve从原本的upward变为flatten说明短期利率上升长期利率下降，远期我们不看，只看近期，所以利率上升，Callable option value不变，请问错哪了？