When is a 21-gun salute rendered?

The 21-gun salute is a traditional military honor that is rendered on specific occasions to recognize significant events or individuals, especially those of national importance. This salute is typically fired as a way to show respect and signifies the highest level of ceremonial honor.

The correct answer encompasses various major national holidays and formal occasions, including Washington's Birthday, Memorial Day, and Independence Day, as well as to honor the President of the United States and heads of foreign states. Each of these occasions holds a significant place in American culture and history, thus warranting the highest military tribute of a 21-gun salute.

By including both national observances and distinguished individuals in this option, it highlights the importance of the salute as a symbol of respect and recognition within naval and military ceremonies. Factors such as honor and tradition play a very crucial role in when this salute is performed, making option C the accurate choice.