Answer: C) Reference.
Step-by-step explanation: A pronoun is a word used to take the place of a noun. Sometimes it is unclear what noun is anteceding the pronoun, this is called a reference error. In the given sentence we can see an example of this kind of error, because the pronoun "that" which should replace the noun "paintings" is misplaced, the correct sentence would be: The paintings that I finished are in the hallway.