What is the difference between 'essential functions' and 'marginal tasks' of a job?

What is the difference between 'essential functions' and 'marginal tasks' of a job?

• A. Marginal tasks are the core duties; essential functions are optional.
• B. Essential functions are the core duties; marginal tasks are incidental duties not central to the job.
• C. Essential functions can be ignored when not busy.
• D. Both are equally central.

Answer: (B)