Which of the following are unfair labor practices by the employer?
a. Employer A decides to have a more friendly labor force. As a result, employer A decides to hire only those who have a negative attitude toward unions.
b. During negotiations, union B asks employer A for contributions to the union fund. As a result, the employer adamantly refuses to bargain on such an issue.
c. Employer D breaks off relations and refuses to bargain with union D ever again because the union asked for a union shop clause.
d. a and c.