Final answer:
The yield curve naturally slopes upwards due to expectations of higher future interest rates.
Step-by-step explanation:
The yield curve naturally slopes upwards due to expectations of higher future interest rates (C). When the yield curve slopes upwards, it means that long-term interest rates are higher than short-term interest rates. This occurs because investors expect interest rates to rise in the future, so they demand higher yields on long-term bonds to compensate for the potential loss of value if rates increase.