Use the liquidity premium to give an explanation for why yield curves have most often been upward

Question:

Use the liquidity premium to give an explanation for why yield curves have most often been upward sloping over the past 50 years. Could a yield curve be upward sloping even if short- term rates were expected to remain constant? If interest rates are expected to fall dramatically, under what conditions would the yield curve still be upward sloping? Yield to Maturity (Percent) 5 Observed Yield Curve (C)= Expectations + Liquidity Premiums (C = A + B) 1 N. 2