Read the passage. 1) Sosi left her backpack on the stool, and it disappeared. 2) Ana thought she saw the backpack near a worktable in the science lab. 3) She was right. 4) The teacher had moved the backpack so that a student could use the stool. 5) Sosi was glad to have her backpack back and thanked Ana for finding it. Which sentence contains an error in pronoun-antecedent agreement?