问题如下：
XYZ company has issued a 4-year semi-annual callable bond with a coupon rate of 8%, the bond's current price is 105. The first call date is at the end of the second year after issuance and the call price is 103. What`s the bond's annual yield-to-first-call?
选项：
A. 3.36%
B. 2.67%
C. 6.71%
解释：
C is correct.
PV= -105, N=4, PMT=4, FV=103,CPT I/Y=3.3567%
The annual yield-to-first-call=3.3567%×2=6.7133%
PMT为什么是4呢，怎么计算出来的
