Paul Wilken works in the structured product group of a large investment bank. One of his new tasks is to perform valuation analysis on mortgage-backed (MBS) and asset-backed securities (ABS). Wilken needs to familiarize himself with the many measures used to value these types of securities. The first valuation metric that Wilken is to explore is the cash flow yield. Wilken would like to determine the strengths and weaknesses of the cash flow yield. Which of the following assumptions is least likely a limitation of the cash flow yield measure?
　　A. The credit risk associated with the underlying loans is constant over the life of the security.
　　B. The computation includes an assumption about the default rate of the underlying loans.
　　C. Similar to the yield to maturity measure all interim cash flows are reinvested at the cash flow yield.
　　D. MBS or ABSs are held until the final payout based on some prepayment assumption.
　　Answer:A
　　The cash flow yield measure does not rely on any credit risk assumption.