A Major Concern Regarding Experimental Research in the Field of Sociology

A major concern regarding experimental research in the field of sociology of religion, and the reason why so little experimental research has been conducted in this field is:

A) Religious groups have been very closed systems and have not let researchers do experiments on them.
B) The ethical issues involved with experimenting in this area are enormous.
C) Experimental research in the area of religion is so expensive to conduct that few researchers have the funds to conduct their experiments.
D) Researchers have had little success finding subjects to allow them to experiment with their religion.