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　　A pass-through mortgage-backed security (MBS) has an effective duration of 10.0 years. The security is structured into two bonds: an interest-only strip and a principal strip. Which of the following statements is not true?
　　A.     As the PSA increases, the value of the principal-only bond will increase.
　　B.     As the PSA increases, the value of the interest-only bond will  decrease.
　　C.     The duration of the IO strip is likely to be negative, even substantially negative.
　　D.     The  convexity of the MBS is likely to be negative, when interest rate rises.
　　Answer: D
　　The convexity of the MBS is likely to be negative when interest rate falls.