The false statement is B.

• A is true: storage costs enter the cost-of-carry model like a negative income yield.
• B is false: convenience yield is a feature of consumption commodities, not investment assets. Investment assets do not typically have a convenience yield.
• C is true: a higher lease rate acts like income from holding the metal and tends to reduce the forward price, contributing to backwardation ceteris paribus.
• D is true: normal backwardation in a consumption commodity can arise from convenience yield and/or risk premia associated with systematic risk.

So the incorrect proposition is B.