Final answer:
The best way to sell the green socks is to offer them to customers while ringing them up, as it actively engages the customer at the point of sale.
Step-by-step explanation:
To sell 15 pairs of green socks at a sporting goods store for $3.00 each, the best action would be option (b): offer them to each customer while ringing them up. This approach is direct and engages the customer at the point of sale, where they are already in the mindset to purchase. Options (a), (c), and (d) are less effective because they either rely on chance (a customer needing green socks or using them to try on shoes) or do not actively promote the item (just decorating the store with a green theme).