这题不太理解，可以解释下吗？

问题如下：

In a mortgage pass-through security, the pass-through rate:

选项：

A.is adjusted as market rates rise or fall. B.adjusts the rate on the underlying pool of mortgages by a servicing fee. C.is equal to the mortgage rate on the underlying pool of mortgages.

解释：

B is correct. In a mortgage pass-through security, the pass-through rate is less than the mortgage rate on the underlying pool of mortgages by an amount equal to the servicing (and other administrative) fees.

A is incorrect because in a mortgage pass-through security, the pass-through rate is less than the mortgage rate on the underlying pool of mortgages by an amount equal to the servicing (and other administrative) fees.

C is incorrect because in a mortgage pass-through security, the pass-through rate is less than the mortgage rate on the underlying pool of mortgages by an amount equal to the servicing (and other administrative) fees.

考点：pass-through rate

解析：pass-through rate是在WAC的基础上扣减掉服务费来的，所以pass-through rate往往低于基础抵押贷款池的抵押利率。因此，B选项正确。