Riots do occur more often on hot days than on cool days (Carlsmith & Anderson, 1979). The hotter the day in a number of cities, the more violent crimes occur (Anderson & Anderson, 1984; Rotton & Frey, 1985). These results suggest that discomfort can lead to aggression. However, such results should be interpreted with caution because

A) the results apply only to urban areas.
B) researchers only studied violent aggression.
C) researchers only studied instrumental aggression.
D) some third variable might account for the relation.
E) researchers limited themselves to the United States.

D) some third variable might account for the relation.