The correct answer is option 3, Second Continental Congress.

The Second Continental Congress was a convention of delegates from the original Thirteen Colonies of America. It convened in Philadelphia, Pennsylvania, from 1775 to 1781. This Congress served as the governing body of the colonies during the early stages of the American Revolutionary War against Great Britain.

It was during the Second Continental Congress that the American Declaration of Independence was adopted on 4 July, 1776. This declaration proclaimed the colonies` independence from British rule and laid the foundation for the United States of America as an independent nation. The document was primarily drafted by Thomas Jefferson, but it underwent several revisions and was approved by the members of the Congress.

The other options listed in the question are incorrect. The Washington Conference and San Francisco Conference were both diplomatic conferences held in the 20th century and had no connection to the American Declaration of Independence. The First Continental Congress, on the other hand, took place in 1774 and was a precursor to the Second Continental Congress, but it did not adopt the Declaration of Independence.