Answer:
Among serial killers, females are known as the "quiet killers", in certain studies, females represent around 8 to 5 % out of all serial killers, and the number of female offenders has significantly decreased since around 1975 compared to male offenders cases which has remained almost the same.
The most suitable answer for the question above would be (a) .
Female serial killers tend to kill over a longer period of time than their male counterparts.