Please choose the correct answer to the question: Which pair of items will repel each other?

Answer1: a positively-charged wool sock and a neutral plastic bag Answer2: a neutral cotton sweater and a negatively-charged plastic pellet Answer3: a negatively-charged balloon and a positively-charged piece of paper Answer4: a negatively-charged plastic strip and a negatively-charged piece of cloth

Answer format: answer1/answer2/answer3/answer4
Answer: answer4