(Last Word) Which of the Following Best Explains Why There

(Last Word) Which of the following best explains why there may exist a negative lower bound for interest rates, beyond which lowering interest rates is counterproductive?

A) Depositors will be willing to accept small negative interest rates in exchange for the convenience of being able to make electronic transactions.
B) The rate of deflation that one would expect at the negative lower bound would keep real interest rates at or above zero.
C) Because of the premium that banks charge on loans over what they pay depositors, up to a point they are always guaranteed to earn a positive rate of interest.
D) Negative lower bounds refer only to real rates of interest, not nominal rates.