Question: Which monorail used to begin the monorail that is a 3.9 mile long monorail mass transit system?
Sentence (from "Mark IV monorail"): Ten trains were built by Martin Marietta in 1969 at the cost of about $7 million USD each and they were used on the Walt Disney World Monorail System between 1971 and 1989 before they were replaced by the Mark VI monorail, although a few lasted until 1991.
Relevant evidence: No