问一道题：NO.PZ2016082402000007

A portfolio manager uses her valuation model to estimate the value of a bond portfolio at USD 125.482 million. The term structure is flat. Using the same model, she estimates that the value of the portfolio would increase to USD 127.723 million if all interest rates fell by 30bp and would decrease to USD 122.164 million if all interest rates rose by 30bp. Using these estimates, the effective duration of the bond portfolio is closest to:

选项：

8.38

16.76

7.38

14.77

解释：

ANSWER: C

By Equation: $D^E=\frac{P_--P_+}{2P_0\bigtriangleup y}=\frac{P{(y_0-\bigtriangleup y)}-P{(y_0+\bigtriangleup y)}}{2P_0\bigtriangleup y}$, effective duration is $D^E=\frac{P_--P_+}{2P_0\bigtriangleup y}=\frac{127.723-122.164}{125.482\times0.6\%}=7.38$

term structure is flat代表什么？