106. A U.S. investor has purchased a tax-exempt 5-year municipal bond at a yield of
3.86 percent which is 100 basis points less than the yield on a 5-year option-free
U.S. Treasury. If the investor’s marginal tax rate is 32 percent, then the yield ratio
are closest to:
A. 0.79
B. 1.26
C. 5.68

如题，答案给的是A：Yield ratio = (yield on tax-exempt bond) / (yield of US Treasury)

但是原来做的题目，还有NOTES上例题，yield ratio都是大于1的。所以我选的是B，正好分子和分母对调了。

为什么选A呢？

notes上说分母是benchmark security.可能是US Treasury当做benchmark吧。