Why do researchers studying the migration history of the human population use mitochondrial DNA (mtDNA)to trace migration patterns?

A)mtDNA is inherited from both of an individual's parents.
B)mtDNA has occasional harmless mutations which eventually appear in almost all individuals in a population and are carried with them during migration.
C)mtDNA does not undergo mutations.
D)mtDNA is not carried by migrating members of a population.
E)mtDNA inheritance in humans proves the bottleneck effect.