问题如下：
What are the different assumptions that can be made when calculating the carry roll-down.
选项：
解释：
Carry roll-down can be calculated (a) assuming that forward rates are realized, (b) assuming that the term structure remains unchanged (c) assuming that bond yields remain unchanged, and (d) assuming that estimates made by the investor are realized.
assuming that the term structure remains unchanged 指的是基准利率保持不变吗？
