Need help... A group of students are designing a field study to investigate the length of time a traffic light remains yellow. In the interests of safety, one of the students suggested the following rules:

• Study the traffic lights at intersections where the speed limit is 70 km/h or less.

• Avoid rush hour. Study traffic lights outside of times when people are going to and from work and school.

Indicate how each of these rules may limit the useful data that comes out of the investigation.