Final answer:
A historian's analysis of the September 11, 2001, written on the 19th anniversary of the attack is an example of a secondary source, as it provides interpretation and analysis after the event occurred. option d is answer
Step-by-step explanation:
The example of a secondary source among the options provided is D) A historian's analysis of the September 11, 2001 attack on the World Trade Center written on the 19th anniversary of the attack. This is because secondary sources are those that are written after the fact and provide interpretation, analysis, or a synthesis of primary sources. They are critical for developing a deeper understanding of historical contexts and events.
In contrast, examples A), B), and C) from the options provided, such as an eyewitness account, soldiers' letters, and accounts by participants, are all primary sources. These sources come directly from the time period to which they refer and offer firsthand accounts of the events being described, making them invaluable for gaining immediate insights into the past. option d is answer