Within the Context of Union Security Clauses, Which of the Following

Within the context of union security clauses, which of the following statements is TRUE?

A) While a union will always prefer for a collective agreement to contain a union security clause, an employer is always entitled to refuse to have such a clause.
B) While union security clauses are permitted in Manitoba, Ontario, and the Maritime provinces, they are statutorily prohibited in the three western-most provinces.
C) A union shop is sometimes called an "agency shop."
D) The purpose of a union security clause is to ensure that employees have job security in accordance with their years of seniority.
E) The "Rand formula" refers to a requirement for all employees to pay into a union whether or not they are members of that union.