不理解这道题

问题如下：

Assume you are using a GARCH model to forecast volatility that you use to calculate the one-day VAR. If volatility is mean reverting, what can you say about the T-day VAR?

选项：

It is less than the $\sqrt T\times$one-day VAR.

It is equal to $\sqrt T\times$one-day VAR.

It is greater than the $\sqrt T\times$one-day VAR.

It could be greater or less than the $\sqrt T\times$one-day VAR

解释：

If the initial volatility were equal to the long-run volatility, then the T-day VAR could be computed using the square root of time rule, assuming normal distributions. If the starting volatility were higher, then the T-day VAR should be less than the $\sqrt T\times$ one-day VAR. Conversely, if the starting volatility were lower, then the T-day VAR should be more than the long-run value. However, the question does not indicate the starting point. Hence, answer d. is correct.