Isaac is researching abraham lincoln’s life for a social studies report. he finds an encyclopedia that includes original letters and articles found in historical journals. the type of source he is using is primary. first. secondary. tertiary.

secondary.

Explanation:

In primary soruces we found the sources that were the closest to the events, primary sources would be diary entries or journalistic articles about Abraham Lincoln, since he is not studying that, he is reading from a encyclopedia that has already summarized and interpreted those documents his sources is a secondary source, because secondary sources take the primary sources and study them or summariz them.