Correct answer is diary entries by President Carter
.
Explanation:
Third and fourth options are not correct as first of all textbook and encyclopedia are not a primary, but a secondary historical source.
On the other side, diary entries are the best primary source because are written sources from the perspective of someone who participated in certain events, in this case president Carter.
Second option is not correct option, but after the diary journal articles would be also important as are written in the period when certain events happened.
