Final answer:
Under Armour has increased its promotion efforts by partnering with well-known athletes, which is a strategic move to enhance brand recognition and drive sales.
Step-by-step explanation:
In addition to extensive online and outdoor advertising, Under Armour has intensified its promotion efforts by signing such noted athletes as Zhu Ting (volleyball) and Kelley O'Hara (soccer). The correct answer is a) Promotion. This strategy is commonly used by companies to increase brand awareness and sales. By associating their products with high-profile athletes, Under Armour aims to leverage these athletes' popularity and influence to boost their brand's appeal and market presence.