Which of the following statements are correct?

If inflation is expected to increase in the future, and if the maturity risk premium is greater than zero, then the yield curve will have an upward slope

If the maturity risk premium is greater than zero, then the yield curve must have an upward slope

Because long term bond are more risky than short term bonds yields on long term treasury bonds will always be higher than yields on short term t bonds

If the maturity risk premium equals zero, the yield curve must be flat

The yield curve can never be downward sloping