问题如下图：是否可以通过性质判断，spot curve 向上倾斜，f（1,1）就＜f（2,1）？
选项：
A. 
B. 
C. 
解释：
NO.PZ2018123101000002 问题如下 Spot curve shows: r(1) = 3.5%, r(2) = 4.5%, anr(3) = 5.6%. Accorng to the spot rates, the forwarrate for a one-yelobeginning in one yewill be: A.less ththe forwarrate for a one-yelobeginning in two-years. B.greater ththe forwarrate for a two-yelobeginning in one-year. C.greater ththe forwarrate for a one-yelobeginning in two-years. A is correct.考点通过Spot rate计算Forwarrate解析通过Spot rate计算Forwarrate的公式，从第1年末开始的一年期Forwarrate为(1+S2)2=(1+S1)(1+f(1,1))1{(1+S_2)}^2=(1+S_1){(1+f(1,1))}^1(1+S2)2=(1+S1)(1+f(1,1))1;代入数据，可得f(1,1)为: 5.51%;对于Af(2,1)为(1+S3)3=(1+S2)2(1+f(2,1))1{(1+S_3)}^3={(1+S_2)}^2{(1+f(2,1))}^1(1+S3)3=(1+S2)2(1+f(2,1))1；代入数据，可得f(2,1)为: 7.84%因此A正确；C错误；对于Bf(1,2)为f(1,2)2×(1+3.5%)=(1+5.6%)3f(1,2)^2\times(1+3.5\%)=(1+5.6\%)^3f(1,2)2×(1+3.5%)=(1+5.6%)3可算的f(1,2)=6.7%，因此B错误。 这道题如果不计算，有没有定性结论？
算f(1,1)时，能不能用 (1.045)^2 * (1+f(1,1)) = (1.056)^3 => f(1,1)=7.83%，为何这样算不行？
