police at a sobriety checkpoint in Riverside pulls over every fifth care to determine whether the driver is sober. Identify the population. _________ (options: Residents of the Riverside county, Police at the sobriety checkpoint, Sober drivers, Drivers in Riverside) and sample. _________ (options: Every fifth driver at the check point, Drivers in Riverside, Sober drivers, Police at the sobriety check point, Resident's of Riverside county) In the study.