A local bookstore experienced a 15% increase in online sales after redesigning its website to be more user-friendly and visually appealing. The owner concludes that the redesign directly caused the increase in online sales. Which of the following, if true, most strengthens the owner's conclusion?
✓ Correct Answer: Option B
By ruling out an alternative cause (new marketing campaigns), this option strengthens the conclusion that the website redesign was the direct cause of the sales increase, as no other significant factors contributed.