Under a 200% PSA model, what is the single monthly mortality(SMM) for, respectively, month 10 and month 30?
　　A. 0.12% and 0.36%
　　B. 0.17% and 0.51%
　　C. 0.28% and 0.65%
　　D. 0.34% and 1.06%
　　Answer:D
　　The base PSA model assumes that prepayments begin at a rate of O.2% CPR in the first month and increase at a rate of O.2% CPR per month until they reach 6.0% CPR in month 30.
　　CPR = 1-(1-SMM)^12 => SMM = 1-(1-CPR)^(1/12)
　　At month 10, 100%PSA = O.2%*10 = 2.0%
　　Therefore, at month 10, a 200%PSA = 4.0% => SMM = 1 一(1-4.0%)^(1/12)=0.34%
　　At month 30, 1OO%PSA = 0.2% * 30 = 6.0%
　　Therefore，at month 30, a 200%PSA = 12.0% => SMM=1 一(1-12.0%)^(1/12)=1.06%