A researcher found that clients who were randomly assigned to same-sex groups participated more in group therapy sessions than clients who were randomly assigned to coed groups. In this experiment,...

A researcher found that clients who were randomly assigned to same-sex groups participated more in group therapy sessions than clients who were randomly assigned to coed groups. In this experiment, the independent variable was:

A. the amount of participation in the group therapy sessions.

B. whether or not the group was same-sex or coed.

C. the clients’ attitudes toward group therapy.

D. how much the clients’ mental health improved.