An analyst does research about price-discount rate relationship. With respect to the price-discount rate relationship, which of the following statements is least accurate（）
A. The shape of the price-discount rate relationship for an option-free bond is referred as negative convex.
B. If the discount rate rises, the price of a putable bond declines by less than the price of an option-free bond.
C. If the discount rate falls, the price of acallable bond increases by less than the price of an option-free bond.
