For which of the following securities is estimating the future cash flows least difficult（）

A. 5-year, 6% bond with two years of call protection.

B. 3-year note with a coupon of Libor + 100 basis points.

C. 8% preferred stock with mandatory redemption in five years.

作用阀管座有3根管子，分别是：3-总风缸；12-制动缸管；14-作用管。