Please choose the correct answer to the question: Which of the following describes a reason why companies irradiate some fruits and vegetables before they are sold to the public?

Answer1: to improve the flavors by increasing the sugar content Answer2: to speed up the ripening of produce picked too early Answer3: to partially cook the produce before canning or freezing Answer4: to extend the shelf life by killing existing microorganisms

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