XV. Nexturn Corporation employed Nini and Nono, whose tasks involved directing and supervising rank-and-file employees engaged in company operations. Nini and Nono are required to ensure that such employees obey company rules and regulations, and recommend to the company's Human Resources Department any required disciplinary action against erring employees. In Nextum Corporation, there are two independent unions, representing rank-and-file and supervisory employees, respectively. a) May Nini and Nono join a union? (2.5%) b) May the two unions be affiliated with the same Union Federation? (2.5%)