A book has disappeared from the classroom shelf. Ava, Liam, Grace, and Sam were the only ones in the room. One of them took it. Exactly one of them is lying.

1. Ava says: "It was Liam."
2. Liam says: "It wasn't me."
3. Grace says: "Liam took the book."
4. Sam says: "I didn't do it."