A researcher uses an anonymous survey to investigate the firearms training of American police officers. Based on the set of 56 surveys that were completed and returned, the researcher finds that these police officers spend an average of 4.1 hours each month for firearms training.
1. For this study, the set of 56 police officers who returned surveys is an example of a(n) ___________.
Options:
A) parameter
B) statistic
C) population
D) sample