You Examined the IQ Scores of Children at Several High

You examined the IQ scores of children at several high schools.You finally select two high schools where the children appear similar in terms of IQ scores,family income,religion,and the like.You match two classes from each grade (9 to 12) from each high school.In one high school you plan to offer a course on study skills in the selected classes and in the other high school you plan to have students follow their "normal" curriculum.After obtaining permission from the principals,parents,and children to do your research,you arrive at the first school to begin the study skills class.You find that the classes you had selected are on field trips and that the principal has assigned another class of the same grade level to you.This class switch illustrates the problem(s) of

A) logistics.
B) administrative control.
C) ethics.
D) logistics, administrative control, and ethics.
E) logistics and administrative control.