In recent years, sales of Lipstick Cosmetics have increased significantly, while the brand's advertising costs have also increased significantly. Industry insiders believe that the increase in sales of Lipstick Cosmetics is due to its promotional role in advertising. Which of the following, if true, would most weaken the conclusion? ['advertising costs of Lipstick cosmetics, not more than other cosmetics.', "few of the buyers of Lipstick cosmetics notice the brand's ads.", 'very few people noticed the ads of Lipstick cosmetics.', 'in recent years, the total sales of cosmetics have increased significantly.']