Students of Psychology Are Often Frustrated Because There Are Very

Students of psychology are often frustrated because there are very few,if any,clear-cut answers to many of their questions.What is the primary limiting factor in obtaining first-hand knowledge of questions such as the long-term effects of child abuse or the effects of smoking marijuana on a pregnancy?

A) Most people in the general public are not concerned with these issues.
B) It is difficult to find people who are victims of abuse or mothers who smoke marijuana during pregnancy.
C) Ethical guidelines in research prevent psychologists from carrying out many of these studies.
D) Institutional review boards encourage participation in studies that may be harmful to subjects either mentally or physically.