Final answer:
The correct answer is option A.Shays' Rebellion.
Step-by-step explanation:
The rebellion being referred to in the excerpt from George Washington's letter to Henry Knox in February 1787 is Shays' Rebellion. This rebellion was an armed uprising in Massachusetts, where discontented farmers, including veterans of the American Revolutionary War, protested against state and local enforcement of tax collections and judgments for debt.
The rebellion is a significant part of American history because it highlighted the weaknesses of the Articles of Confederation and the need for a stronger national government, leading to the Constitutional Convention and the creation of the U.S. Constitution.