A Closed Shop and a Union Shop Differ Primarily in That

A closed shop and a union shop differ primarily in that

A) nonunion workers can retain employment in a union shop, but not in a closed shop
B) nonunion workers can retain employment in a closed shop, but not in a union shop
C) union members are not permitted to work in a closed shop, and a worker must be a union member to work in a union shop
D) in a closed shop, workers must be union members before they are hired but not in a union shop
E) workers must first be union members to work in a union shop