Use the graph to answer the question. The graph shows the relationship between the time and the speed of a train that has already left the station.
Train Speed
Speed (miles per hour)
100-
90-
80+
70
60-7
50+
40
30
20
10
0
10 20 30 40 50 60 70 80 90 100
Time (minutes)
During which time period was the train traveling at a constant speed?
O B. between 20 and 40 minutes
O A between 0 and 20 minutes
Oc between 40 and 60 minutes
O D. between 60 and 80 minutes