The term essential function of a job, as used in the Americans with Disabilities Act $($ADA$),$ best refers to:

Tasks so designated by an employer as ancillary to the achievement of the job's long$-$term goals

Tasks so designated by the Equal Employment Opportunity Commission $($EEOC$).$

Those tasks that are required to be performed in case of any emergencies

Those tasks that are fundamental and not marginal or unnecessary to fulfillment of the job's objectives