Under 46 CFR §185.420, how frequently must crew members receive emergency training at minimum after their initial instruction?

Why C is correct

46 CFR §185.420(a) requires the owner, charterer, master, or managing operator to instruct each crew member upon first employment and at least once every three months thereafter regarding emergency duties. Monthly egress training is an additional requirement only for certain vessel types under §185.420(b)(3).