The yield curve is a graphical representation of the term structure of interest rates. Yields fall as maturity lengthens.
Yields remain constant as maturity lengthens.
Yields rise as maturity lengthens. The risk curves are graphical representations of the risk structure of interest rates relative to the yields on risk-free securities. The least risky securities, because the federal government can print money or levy taxes to pay off its debt. The next least risky securities, because state and local governments can levy taxes to pay off their debts. The most risky securities, because corporations can depend only upon their revenues to pay off have only their debts.