Which feature must the top of vertical supports be anchored into?

The correct answer is concrete, as it provides a stable and durable foundation for vertical supports. When vertical supports are anchored into concrete, they gain significant resistance against lateral forces, which is essential for stability in various conditions such as wind or when experiencing load shifts. Concrete is a strong material that helps ensure the integrity and longevity of the structure being supported.

Options like wooden logs, steel plates, and ground stakes may not offer the same level of support or stability. Wooden logs can decay over time and might not be suitable for load-bearing applications. Steel plates can be beneficial in some contexts, but without being anchored properly into a solid base like concrete, they may not provide the necessary support. Ground stakes are typically used for temporary or less robust structures and do not offer the same permanent stability as a concrete anchor. Thus, concrete is the preferred choice for securely anchoring vertical supports.