之前做过的例题，就说如果半年付息一次，6月30日的cpi要到12月31日生效调整。这题为何是cpi一变化，coupon rate立刻调整了？谢谢
问题如下图：
选项：
A. 
B. 
C. 
解释：
NO.PZ2018062010000001 问题如下 Suppose tha country in Australia issuea 15-yecapital-inxebonwhiha link to the Consumer PriInx(CPI). The pvalue w2,000 anthe coupon rate w6%. The wof the interest paithe bonwsemi-annually. Assuming ththe bonwissuein half a yeago, toy’s CPI is crease5%. So, in toy, whiof the following best scribes this bon A.The principrepayment creases to 1,950. B.The first coupon payment of the bonis 57. C.The coupon rate of the boncreases to 5.7%. B is correct.Accorng to the concept of the capital-inxebon although the coupon rate will not change, the coupon payment will change with the increase or crease of the principamount whipen on the increase or crease of the inx. We cknow ththe CPI creases 5%, it lea to the principamount also creases 5% whiis 2,000 x (1 – 0.05) = 1,900. Although the coupon rate will not change whiis 6%, the first semi-annucoupon payment is (1,900 x 0.06) / 2 = 57 with the use of the new principamount.考点capital-inxebon析capital-inxebon债券的面值会随着通货膨胀率而调整。CPI下降5%, principamount也下降5%。面值调整为2000*（1-5%）=1900，故A不正确。其coupon rate不会发生改变，注意这个债券是半年付息一次，因此，每一期的coupon rate为6%/2=3%，故C不正确。第一期的coupon payment为1900×3%=57，B正确。 A，时间不是才半年吗？
NO.PZ2018062010000001 a正确的话应该是多少，怎么算的
这道题能做对，想问一下这种情况下将来归还的本金是2000还是1900？
可以理解为CPI是随时调整面值的吗？比如发COUPON前一天调整了面值，coupon就按照新的面值计算？
