I think the best option is: B) As a persuasive device encouraging students to vote in a school election.
As you can see in the image a girl is putting her vote in the ballot box. We can observe that she is young so she is probably a student participating in a school election. Her atitude is positive, she is making thumbs up, in this way the photo is showing us that voting can be an enjoyable experience.
The presentation is trying to make the students feel identified with this photo that presents someone their age.
I don't think that the other options are represented in the photo. It doesn't give enough infortmation to compare the candidates as you can see only a voter. A timeline for voting requires the image of a calendar for example.
