What Makes One Louse Able to Survive Treatment with Permethrin

What makes one louse able to survive treatment with permethrin and another louse unable to survive?

A) If there is genetic variation in the louse population independent of permethrin exposure, then some lice are likely to be resistant.
B) If a louse is exposed to low levels of permethrin, then it becomes resistant.
C) If the parents of a louse are exposed to permethrin, then the offspring become resistant.
D) If a louse is exposed to other anti-lice treatments, then it becomes resistant to all anti-lice treatments.