E.  What to do if nominal rates fall to zero? If a target for price level, positive inflation rate, or average inflation rate had not been implemented and made credible before a central bank was confronted by zero nominal interest rates, the central bank could, of course, introduce them at that time. However, such a move might lack credibility.
It might be seen as an emergency program that might not be sustained once the economy recovered and moved away from the zero nominal bound. Moreover, with prices falling and the economy in recession, one could imagine a good deal of skepticism about the ability of the central bank to meet its objective.