Answer:
D. a love letter written to John Adams from Abigail Adams.
Step-by-step explanation:
When you are conducting research, you will need to use a variety of sources to obtain information on the topic you are researching. These sources will be divided in primary and secondary sources. Primary sources are those that were created at the same time as the event you are studying. They are created by people who had a direct connection with the event, and are first-hand accounts of it. An example would be this love letter.