In a Study of Illicit Drug Use and Attempted Suicide

In a study of illicit drug use and attempted suicide the crude relative risk is 2.1 overall but it is 3.4 for men and 1.3 for women when the sexes are considered separately.
This suggests that:

A) There is confounding by sex in these data
B) There is confounding by some unknown or unmeasured factor in these data
C) There is evidence of effect modification by sex in these data
D) The results have been adjusted for age and sex
E) The results are due to bias