Which letter is used incorrectly?

A. Dressage is a form of equestrian competition that requires subtle guidance of a horse through complex maneuvers.

B. Equestrian troops are inefficient in modern warfare.

C. A race horse can be trained to be an obedient equestrian.

D. In the Louvre in Paris you can see a ninth-century equestrian statue of the French Emperor Charlemagne as well as the portrait of Mona Lisa.

The word is equestrian.