What is the signal series in Tunnel E?

The correct answer reflects the established standards for signal series within the context of Tunnel E. The signal series generally refers to a designated range or set of numbers that are used for categorizing and identifying signals, often based on their operational or technical characteristics. In this context, the series identified as 200 even is significant, as it aligns with the specifications or protocols relevant to Tunnel E operations.

Specifically, the choice of the 200 even series suggests that it may either correspond to a specific class of operations, a safety standard, or a regulation governing signaling in tunnels of this design. This choice may also indicate that these signals are standardized in a way that facilitates processing, response, or safety within the tunnel environment.

Understanding the importance of the correct signal series is crucial for maintaining communications, ensuring safety protocols are followed, and managing the operational flow in the tunnel efficiently. Each signal series likely has defined purposes and applications within tunnel operations, contributing to the overall safety and efficiency of the infrastructure.