Which sentence corrects the error in pronoun-antecedent agreement?

They had a hard time choosing the topic of their project.
Students can research any subject they are interested in as long as our subject is related to the city’s history.
We included a lot of photographs in his presentation.
I plan to take our own pictures of interesting old buildings around the city.

Pronoun-antecedent agreement refers to the correspondence in number that must be between the subject and its antecedent, which is the noun that the pronoun replaces. As a result, a singular pronoun must coincide with a singular antecedent, while a plural pronoun must correlate with a plural antecedent.

The rest of the choices must be revised like the following:

Students can research any subject they are interested in as long as their subject is related to the city’s history.
We included a lot of photographs in our presentation.
I plan to take my own pictures of interesting old buildings around the city.