Which is an example of the bystander effect?
A. Of all the people in the park on Sunday, only two of them choose
to use the hiking trail.
B. People work together in groups to clean up a park so that it can be
used by children who live in the surrounding area.
C. Of the 100 people who witnessed a crime in a local park, no one
reported it.
D. Hundreds of people use a park's facilities every day, and very few
crimes are committed on the park grounds.