context: The main part of the system was built in the 1950s and 1960s; the construction was completely completed in the 1980s. The length of the line, along with all branches, is slightly less than 25 km. Depth of laying - from 50 meters in the center to 210 meters in the area of ​​the NIBO "Science"
question: What is the length of the secret Moscow underground transport facility Metro-2?
answers.text: 25 km