What Barrier Do Researchers in the U

What barrier do researchers in the U.S. face in the effort to study gun violence?

A) Congress prohibits federal money being used to study the social effects of guns.
B) Social researchers are uninterested in the topic.
C) Social researchers who have studied guns in the past have been harassed, so researchers now are hesitant to do it.
D) The social aspects of gun ownership in the U.S. are relatively stable, so no new research is needed.