Question: Besides the length of Charles Grethen's primary race event, which two race lengths are standard in middle-distance running?
Sentence (from "Middle-distance running"): The 1500 m came about as a result of running three and 3/4 laps of a 400 m outdoor track or 7 and a half laps of a 200m indoor track, which were commonplace in continental Europe in the 20th century.
Relevant evidence: No