问题如下：
Southwest Capital Advisors LLC manages a fixed-income composite in accordance with an enhanced indexing strategy which makes strategic use of high-yield and emerging market bonds in addition to investment grade bonds issued in developed markets. The Merrimack Company, a family office, has a portfolio that is included in the firm’s fixed-income enhanced indexing composite. Merrimack informs Southwest in writing that, due to changes in its investment policy, the portfolio can no longer hold high-yield or emerging market bonds. In accordance with the GIPS standards, Southwest decides to switch the Merrimack portfolio to another composite. The historical performance of the portfolio must be:
选项：
A.reflected in both composites.
B.switched to the new composite.
C.retained in the enhanced indexing composite.
解释：
C is correct.
Provision I.3.A.7 states, "Portfolios must not be switched from one composite to another unless documented changes to a portfolio’s investment mandate, objective, or strategy or the redefinition of the composite makes it appropriate. The historical performance of the portfolio must remain with the original composite." (See Section 3.9 of the reading.)
请问这道题目的答案说除非“unless documented changes to a portfolio’s investment mandate, objective, or strategy ”，除非以上发生才可以switch到其他的composite中，同时题目中提到investment policy已经改变了，那不就可以switch了吗？否则考试的时候如何判断，真的发生了investment mandate的改变了呢。谢谢
