Which of the following statements correctly describes the relationship between spans in OpenTracing?

The correct answer highlights that a call chain is a directed acyclic graph composed of multiple spans. In OpenTracing, spans represent individual units of work within a certain operation in a distributed system. Each span can have a parent-child relationship with other spans, and when these spans are connected, they can visually and logically create a call chain.

This structure forms a directed acyclic graph (DAG) where each span may depend on others, forming a hierarchical representation of how different operations are executed and how they interact with one another over time. This effectively captures the flow of requests and the duration it takes to complete various operations in a distributed environment, which is crucial for diagnosing performance issues and understanding data flow.

This understanding helps developers trace the sequence of calls through the system, allowing them to optimize performance and troubleshoot failures more effectively. The recognition of spans forming a directed acyclic graph is critical in comprehending how tracing works in large, complex systems.