请问这道题的delta T等于多少，我看题里面写的一年我就用的250

问题如下：

A stock is currently trading at USD 45, and its annual price volatility is 30%. The risk-tree rate is 1.5% per year. A risk manager is developing a 1-step binomial tree for a 2-year horizon. What is the risk-neutral probability that the stock will move down?

选项：

A.

30%

B.

43%

C.

57%

D.

70%

解释：

$P=\frac{e^{rt}-d}{u-d}=\frac{e^{1.5\%\times2}-0.65}{1.52-0.65}=0.4373\\u=e^{\sigma\sqrt t}=e^{30\%\times\sqrt t}=1.52\\d=\frac1u=0.65\\1-P=56.27\%$