Final answer:
Online discounts from competitors are the likely cause of declining wallpaper sales for Contemporary Trends, as they appeal to modern consumers' preference for convenience and savings.
Step-by-step explanation:
The likely cause of the decline in wallpaper sales for Contemporary Trends is b) Online discounts offered by competitors. As noted, the internet has had a significant impact on traditional brick-and-mortar businesses. Companies advertising online can reach a broader audience with discounted prices, free shipping, and convenient toll-free ordering. This modern convenience has overshadowed traditional in-store shopping experiences, impacting sales of retail items like wallpaper. With the introduction of online shopping and advertising, consumer habits have shifted considerably since the presence of earlier models like mail-order houses and department stores.