An investment policy statement for a firm’s short-term cash management function would least appropriately include :（）

A. a list of permissible securities.

B. procedures to follow if the investment guidelines are violated.

C. limits on the proportion of the portfolio which can be invested in each permitted security type.

往水样中投加一些化学试剂(保护剂)可固定水样中某些待测组分，经常使用的水样保护剂有各种（），加入量因需要而异。

A、酸

B、碱

C、盐

D、生物抑制剂