When was the Declaration of Independence adopted?

The Declaration of Independence was adopted on July 4, 1776, which is why this choice is the correct answer. This date marks a pivotal moment in American history, as it represents the formal assertion of independence from British rule, where the American colonies declared themselves free and independent states. The adoption of the Declaration of Independence is celebrated annually in the United States as Independence Day, a significant national holiday.

The other dates provided are significant in their own contexts but do not relate to the Declaration of Independence. For instance, April 6, 1776, does not correspond to any important milestone associated with the declaration. June 21, 1776, also lacks historical relevance in this context. September 17, 1787, marks the signing of the United States Constitution, which is a separate foundational document for the government rather than the declaration of independence itself. Understanding these historical landmarks is essential for grasping the chronological development of American independence and governance.