The only article among these options is an, and that is the correct answer - <em>an </em>is the indefinite article.
It, her, and that are pronouns.
When my cousins come to visit, we put an extra leaf in the table to make it bigger.
Problem: Cousins coming to visit = more people to fit in the desk
Solution: putting an extra leaf
I don't know but a long essay or dissertation is involving personal research, written by a candidate for a college degree.
C. Using vivd language and sensory details to create images.
It would imply that the conspirators flattered Caesar mostly out of fear