What is meant by the term bystander effect? A. People tend to have more fun when they are in groups instead of
being alone.
B. People can find that a group may be too large to have any
cohesiveness.
C. Individuals may have difficulty describing a person who
committed a crime.
D. Individuals tend to take more responsibility for reporting crimes
than do groups of people.

D. Individuals tend to take more responsibility for reporting crimes  than do groups of people.

Explanation:

"Bystander effect" is a theory stating that people have the tendency to help others when they are alone rather than when they're in a group. Being in a group creates the so-called "diffusion of responsibilities." This means that the reaction to help will largely depend on other people surrounding them. This creates less pressure because one knows that there are many observers. However, when one is alone, one is more likely to help a person in need because there are no onlookers he's basing his reaction from.