Who was Baron Friedrich von Steuben?

A. A young German officer on Washington's staff who captured a British fort during the battle at Yorktown

B. A former Polish captain who turned a disorderly group of American recruits into skilled soldiers

C. The Hessian commander of British troops in the South who lost the battle of Yorktown

D. The Frenchman who became a general on Washington's staff and his lifelong friend

Please, I need help on this!