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 ana for finding it.

which sentence contains an error in pronoun-antecedent agreement?
sentence 1
sentence 2
sentence 4
sentence 5

I took the test last week and the answer was sentence 1

sentence 1  

Explanation:

A pronoun is, by definition, the substitute for a name. In order for a pronoun to occur, it is necessary that the name before occurs for this pronoun to refer. In the case of sentence 1, the pronoun "it" should be referring to "backpack" or "stool" which are the possible antecedents. The problem is, the way the sentence was written does not allow us to know who the antecedent of "it" is. That is, it is not possible to know if the pronoun is referring to "backpack" or "stool".