The table below summarizes the yields and corresponding price for a hypothetical 15 -year option-free bond that is initially priced to sell at 7% yield: Yield (%)Price ($) 6.90% 100.925 47.00 % 100.0000 7.10% 99.0861 Using a 10 basis point rate shock, the effective duration for this bond closest to:（）
A. 4.6 years.
B. 7.5 years.
C. 9.2 years.