Given:
The three graphs represent the progress of three runners in a 400-meter race.
The solid line represents runner A
The dotted line represents runner B.
The dashed line represents runner C.
To identify the graph which has the constant rate throughout the race:
According to the graph,
The graph which has the constant rate throughtout the race is the dashed line graph.
Since it is a straight line, it has a constant rate.
Hence, runner C ran at a constant rate throughout the race.