Which of the following is an unfair labor practice $($ULP$)$ under the National Labor Relations Act?

$(2$pts$)$

Question $8-$ Which of the following is an unfair labor practice $($ULP$)$ under the National Labor Relations Act?

discriminating against an employee based on her race

violating the terms of a labor agreement

retaliating against an employee who has filed charges with the NLRB

after an agreement has expired and while the new one is being negotiated, locking out employees willing to continue working