Final answer:
Retailers respond to increased mobile device usage by harnessing locational technology to provide targeted services and improve customer engagement.
Step-by-step explanation:
One tactic that retailers have used to respond to the increased use of mobile devices by consumers is E. They are harnessing the power of locational technology. This involves using GPS and other location-based services to provide targeted advertisements, discounts, and product recommendations to consumers based on their physical location. By doing so, retailers can engage with customers in a more personalized manner, often when they are near or in the retailer's physical store, which can boost sales and improve customer experience.