A School Social Worker Administered a Self-Esteem Test to a Group

A school social worker administered a self-esteem test to a group of 9th graders in September.During the school year the students received intensive social work intervention designed to improve their self-esteem.In May the self-esteem test was given again and the self-esteem scores improved.A major problem in this research is that the researcher failed to control for

A) history.
B) maturation.
C) testing.
D) selection biases.
E) all of these.