An inverted futures market is characterized by backwardation, where futures prices are below the spot price and the curve slopes downward with maturity.

• A is true: backwardation describes an inverted market.
• C is true: if $F(0) < S(0)$, the futures price is below spot.
• D is true: if a longer-dated futures price is below a shorter-dated one, the curve is inverted.
• B is the exception in this context because normal backwardation is not the cleanest curve-shape description for an inverted market; it is a separate term and is not the best direct characterization here.

So the best answer is B.