An Example of Unobtrusive Data Collection Is

An example of unobtrusive data collection is:

A) an interview with college freshmen to determine why they selected a particular school.
B) a laboratory experiment designed to learn whether people really prefer Pepsi or Coke.
C) a mailed survey designed to discern students' attitudes toward a planned change in the school's calendar.
D) a researcher who joins a fraternity to understand its rituals.
E) examining the wear on the tires of squad cars to determine the extent of police patrols.