Please choose the correct answer to the question: Roger visited his grandfather who lives on a farm. While he was there, he helped his grandfather move hay out of the barn. As Roger worked in the barn he began sneezing. Which system of the body most likely caused Roger to sneeze?

Answer1: circulatory Answer2: excretory Answer3: digestive Answer4: immune

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