问题如下：
Which of these statements regarding risk factor mapping approaches is/are correct?
I. Under the cash flow (CF) mapping approach, only the risk associated with the average maturity of a fixed-income portfolio is mapped.
II. Cash flow mapping is the least precise method of risk mapping for a fixed-income portfolio.
III. Under the duration mapping approach, the risk of a bond is mapped to a zero-coupon bond of the same duration.
IV. Using more risk factors generally leads to better risk measurement but also requires more time to be devoted to the modeling process and risk computation.
选项：
A. I and II
B. I, III, and IV
C. Ill and IV
D. IV only
解释：
Under the cash flow (CF) mapping approach, each payment (and not only the last one) is associated with a different risk factor, so statement I. is incorrect. Statement II. is incorrect because the CF mapping approach is more correct than duration or maturity mapping.
是principal还是duration mapping 假设了zero-coupon?