Workers have the right to strike but certain kinds of strikes are illegal. Which of the following statements is true? A. If the collective bargaining agreement is for an indefinite period, 30 days notice must be given to the employer. B. If the strike concerns an employers unfair labor practice, 60 days notice must be given. C. If the collective bargaining agreement is for a definite period, a strike may only be called within that period. D. If the collective bargaining agreement is for a definite period, 60 days notice must be given if the union wishes to strike to seek modification of the agreement