Step 1: Concept
In chain surveying, the area is divided into a network of triangles.
Step 2: Meaning
The survey relies on a primary central line that runs through the middle of the area to be surveyed.
Step 3: Analysis
The Base line is the most important and longest line in the survey. It should be measured very accurately as the entire framework of triangles is built around it.
Step 4: Conclusion
The longest chain line is the Base line.
Final Answer: (B)