Which example demonstrates the use of synecdoche?

The example "Boots on the ground" effectively demonstrates the use of synecdoche because it uses a part of something—the boots representing soldiers or military personnel—to refer to the whole concept of troops engaged in combat or military action. This figurative language captures the essence of soldiers being in the field while focusing on a specific part of their equipment. Synecdoche works by allowing a smaller, more concrete element to represent a broader concept, creating a vivid image and conveying complexity succinctly.

Other examples provided do not embody synecdoche in the same way. For instance, "The throne was empty" speaks more generally about a position of power that is unoccupied. "The wheels on the bus" focuses on the whole bus while only mentioning a part, not indicating a representative aspect. "He has a heart of gold" uses metaphor to describe someone kind and generous, but it does not involve the use of a part to represent a whole.