这题不懂求解答，对应知识点是在哪里？

问题如下：

If the level of broad inflation indexes is largely determined by commodity prices, the average real yield on direct commodity investments is most likely:

选项：

A.less than zero. B.equal to zero. C.greater than zero.

解释：

B is correct. As the price increases of commodities are mirrored in higher price indexes, the nominal return is equal to inflation and thus the real return is zero. A is incorrect. A negative real return implies inflation greater than nominal return. This is not the case if commodity price increases determine inflation. C is incorrect. A positive real return implies inflation less than nominal return. This is not the case if commodity price increases determine inflation.