Researchers Believe That Experiencing Strong Negative Emotions Such as Fear

Researchers believe that experiencing strong negative emotions such as fear or anxiety will increase people's need to affiliate.To test this idea,the researchers randomly assigned participants to one of two small groups.Members of Group 1 were left for 10 minutes in a room with no windows.While waiting,the lights went out for a brief period of time and the participants could hear screams from another room.Members of Group 2 were likewise left for 10 minutes in a room with no windows,but the lights were left on and no screams were heard.Researchers observed how frequently members of each group started conversations with other members of their group on non-experiment related topics.Researchers assigned participants to one of the two groups randomly because ________.

A) random assignment eliminates the need for statistical analysis of the results of an experiment
B) random assignment makes sure that unknown characteristics of research participants may cause differences in the dependent variable across the three groups
C) random assignment is the easiest,most cost effective way of assigning group membership to participants
D) random assignment ensures that any changes in the dependent variable are caused only by changes in the independent variable
E) random assignment ensures that no group member knows any other group members before the experiment begins