An officer signals from their vehicle that you must stop on the right side — how do they signal this?

A)With a red flag.
B)With a yellow flag.
C)With the arm extended downward at an angle and held still.Correct
An officer from their vehicle will indicate the obligation to stop on the right side with the arm extended downward at an angle and held still.
In the case of carrying a red flag, it will indicate that the road is temporarily closed to all vehicles and users, except those being escorted by officers.
If the flag is yellow, it will indicate the need to be especially alert or the proximity of a hazard.