18. Ross, a friend of Julie, also operates an online store that sells sport clothes. Like Julie, Ross would like to know whether adding a welcome logo to his old store website helps bring more visitors. When Ross conducts the A/B test, he displays the old store website to randomly selected return customers and shows the new store website (ie., the old store website plus a welcome logo) to randomly selected new customers. Because he believes that return customers are familiar with the old store websites. ~ Does Ross conduct a valid A/B test? Explain your answer. (Hint: If yes, then explain why it is valid; if no, then explain why it is invalid.) (3 points) tettet