Riots Do Occur More Often on Hot Days Than on Cool

Riots do occur more often on hot days than on cool days. The hotter the day in a number of cities, the more violent crimes occur. These results suggest that discomfort can lead to aggression. However, such results should be interpreted with caution because __________.

A) representative samples were not secured by the researchers
B) some third variable might account for the relation
C) researchers only studied violent aggression
D) researchers limited themselves to the United States