An important reason for constructing an investment policy statement is that it:()

A. minimizes the costs of portfolio construction.

B. ensures that managers outperform the performance benchmark.

C. includes a performance benchmark to judge manager performance.

于功率的概念，下列说法正确的是（     ）

A：功率是描述力对物体做功多少的物理量

B：由P＝W/t可知，功率与时间成反比

C：由P＝Fv可知，只要F不为零，v也不为零，那么功率P不一定不为零

D：某个力对物体做功越快，它的功率就一定越大