After Years of Failure, the Employees at the Cherryville Branch

After years of failure, the employees at the Cherryville branch of MegaStore, an international chain of discount stores, finally succeeded in becoming unionized.They are very anxious to ensure that the collective agreement, which is currently being negotiated, does everything possible to solidify their position and to prevent the company from undermining their recent success.Which of the following statements is TRUE with respect to a union security clause?

A) An approach sometimes referred to as an "agency shop" will ensure that the store contains only unionized employees.
B) Under a closed shop clause, MegaStore will be required to allow an employee at another one of its branches join the Cherryville store without having to join the union.
C) The collective agreement will not necessarily include such a clause.
D) It would be unlawful for a collective agreement to prohibit a non-union person from being an employee at the Cherryville branch.
E) Such a clause is relevant only in the event of a grievance.