Which statement best describes the economic problem known as the liquidity trap, where money demand is perfectly elastic to the interest rate?

a. The interest rate reaches a upper bound, and liquidity preferences have fallen to such an extent that people are unwilling to sell interest bearing assets.

b. The interest rate reaches a lower bound, and liquidity preferences have fallen to such an extent that people are unwilling to sell interest bearing assets.

c. The interest rate reaches a upper bound, and liquidity preferences have risen to such an extent that people are unwilling to purchase interest bearing assets.

d. The interest rate reaches a upper bound, and liquidity preferences have fallen to such an extent that people are unwilling to purchase interest bearing assets.

e. The interest rate reaches a lower bound, and liquidity preferences have risen to such an extent that people are unwilling to purchase interest bearing assets.