Choice "D" is correct. The age discrimination in employment act ("ADEA") prohibits age discrimination, whether intentional or unintentional.
Choice "b" is incorrect, because the ADEA does not prohibit termination for cause at any age.
Choice "a" is incorrect, because the ADEA does not prohibit mandatory retirement for employees over 40 if, for example, there is a bona fide occupational qualification.
Choice "c" is incorrect, because the ADEA does not prohibit termination of employees as part of a rational business decision.
