Which of the following is a national U.S. holiday?

Thanksgiving is a national holiday in the United States, celebrated on the fourth Thursday of November each year. It originated as a harvest festival and has evolved into a day of giving thanks and gathering with family and friends to share a meal, often featuring turkey. The holiday is recognized and observed across the entire country, making it part of the American cultural tradition.

Halloween, celebrated on October 31, is not a national holiday; rather, it is more of a cultural observance associated with activities like trick-or-treating and costume parties. Earth Day, celebrated on April 22, is focused on environmental protection and awareness, but it does not hold the status of a national holiday. Valentine's Day, observed on February 14, is primarily a celebration of romantic love and is not considered a federal holiday either.