In Which of the Following Situations Would It Be Legal

In which of the following situations would it be legal for the employees to strike?

A) Ace Manufacturing made armaments and some were sold to South Africa. When the employees found this out, they went out on strike, demanding that the practice stop.
B) The A.F.I.O., the properly certified bargaining agent for the employees of Ace Manufacturing Ltd., were demanding an unreasonably high wage settlement from the employer, which would bankrupt the firm if accepted. The employer refused to agree to this and the employees went out on strike.
C) The A.F.I.O. was approached by a group of employees working for Ace Manufacturing Ltd. to see if they would organize the work force and unionize it. When the employer discovered this, he fired that group of workers and the rest went out on strike.
D) The employer introduced some new policies into the plant that, while they did not violate the terms of the collective agreement in place, were very much resented by the workforce. The employees then participated in a deliberate process of sabotage and slowdown to show their displeasure.
E) A collective agreement was in place between Ace Manufacturing and its employees, and that contract was blatantly breached by the employer, resulting in the employees going out on strike.