Traffic safetynbsphere is a passage from a study published

Question

Traffic Safety: Here is a passage from a study published by the National Highway Traffic Safety Administration in 2007.

"The National Occupant Protection Use Survey (NOPUS) is the only probability-based survey of driver cell phone use in the United States. The survey observes usage as it actually occurs at a random selection of roadway sites, and so provides the best tracking of the extent to which people in this country are using cell phones while driving."

NOPUS observed 43,000 drivers in this study.

Which feature of the sampling plan makes the sample representative of the population?

1. The reputable organization conducting the study (the National Highway Traffic Safety Administration)
2. The large sample size of 43,000 drivers
3. The random selection of roadway sites