RMSE at Headwater

The RMSE for the headwater point at Williamsburg shows that the error gets greater with lead time, with some leveling out after 84 hours.

Root Mean Squared Error (RMSE) of Ensemble Mean Forecast Per Lead Time Interval for Headwater Point at Williamsburg

Question

How does the top 20% of flows (blue line) compare with all flows (red line)? (Choose the best answer.)

The correct answer is c.