What Is the Key Difference Between Mass Murder and Serial

What is the key difference between mass murder and serial murder murder?

A) Mass murders tend to be committed by teams of offenders whereas serial murders are typically committed by offenders working alone.
B) Mass murder involves a cooling-off period between offences whereas serial murder does not.
C) Mass murder involves the killing of at least three people whereas serial murder involves at least six victims.
D) Mass murder involves the killing of individuals at several locations whereas serial murders tend to occur at the same location.
E) Mass murder does not involve a cooling-off period between offences whereas serial murder does.