Which of the Following Elements Constitutes an Affirmative Defense by an Employer

Which of the following elements constitutes an affirmative defense by an employer whose employee has suffered sexual harassment at the workplace?

A) The plaintiff-employee was harassed by other employees who are no longer employed by the employer.
B) The employer had no knowledge about the sexual harassment faced by the plaintiff-employee until a court notice was served on the employer.
C) The plaintiff-employee failed to take advantage of any preventive or corrective opportunities provided by the employer.
D) The plaintiff-employee misinterpreted words or actions by the employer or his employees which were not intended to cause sexual harassment.