问题如下：
Exhibit 2 presents most of the data of a binomial lognormal interest rate tree fit to the yield curve shown in Exhibit 1.
The trader believes that the actual market volatility is higher than the volatility used in Exhibit 2. He wants to update Exhibit 2 to reflect the current volatility, which is now 15%.
If the assumed volatility is changed as the trader requested, the forward rates shown in Exhibit 2 will:
选项：
A.spread out.
B.remain unchanged.
C.converge to the spot rates.
解释：
A is correct.
考点：考察对利率二叉树的理解
解析 ： 将二叉树的波动率从10 ％ 增加到15 ％ 将导致远期利率（Forward rate）在树上扩散开，增加节点之间的宽度。
B不正确，因为波动率是二项利率树模型中的关键假设。波动性的任何变化都会导致二叉树中远期利率的变化。
C不正确，因为将波动率从10 ％ 增加到15 ％ 会导致可能的远期利率在二叉树上扩散。
请问老师：二叉树更spread out 我明白，但是forward rate应该是不变才对，因为par rate不变推出spot rate不变，spot rate不变，forward rate不变。请老师帮看一下哪个环节分析错了。谢谢！
