686 meters
670 meters
720 meters
None of these
Answer is Wrong!
Answer is Right!
The correct answer is A. 686 meters.
A standard BG loop line is a type of railway track that is used in India. It is a single track that is looped back on itself, so that trains can travel in either direction without having to cross each other. The length of a standard BG loop line is 686 meters.
Option B is incorrect because the length of a standard BG loop line is not 670 meters.
Option C is incorrect because the length of a standard BG loop line is not 720 meters.
Option D is incorrect because the length of a standard BG loop line is not none of these.