在FRM 2011 practice exam level I的第15题中提到：

The cheapest to deliver bond on maturity is defined to be the one for which the adjusted spot price is the lowest. Adjusted Spot Price = Spot Price / Conversion factor.
同时又让参考John Hull第7版第6章，但是Hull的书里没提到什么Adjusted spot price。如何理解上面的解释？