An individual firm faces demand that is perfectly elastic at the prevailing price. Average cost is falling for all levels of output. None of the above. There are many buyers and many sellers. There are no barriers to entry.
Economic profit is zero.
The firms produce a homogenous product. An individual buys apples and bananas. Mary spends all of her income on cookies and milk. More computers are being sold today than a year ago, and the price has dropped. Farrell can produce 10 multiple-choice questions or grade 25 exams in one day.