问题如下：
What of the following is the drawback of risk-based approach to asset classification?
选项：
A.It overestimates the portfolio diversification.
It is sensitive to historical look-back period.
It has united risk factor identification.
解释：
B is correct.
The major drawback of risk factor based approach is that it depends on the histocial data and the sepecific data period.
traditional approach 的基本原理是什么？
