Final answer:
The Americans With Disabilities Act of 1990 defines essential job functions as duties that an employee with a disability must be able to perform with or without reasonable accommodation, provided such accommodation does not cause undue hardship to the employer. The correct option is D.
Step-by-step explanation:
According to the Americans With Disabilities Act of 1990 (ADA), the definition of essential job functions when considering the employment of a person with a disability is D. Functions that an employee must be able to complete, with or without a reasonable accommodation. This means that essential job functions are the fundamental duties of a position that an individual with a disability must be able to perform, either on their own or with the help of a reasonable accommodation provided by the employer. The ADA requires that accommodations do not impose an undue hardship on the operation of the business.
The ADA aims to prevent employers from discriminating against qualified individuals based on their disabilities and promotes equal opportunity in employment. Essential job functions are not based solely on what an employer determines to be completed, the physical functions of a task, or the speed at which tasks are performed, but rather on the core duties that are necessary to the position.