Piece workers are paid on the basis of ________.

The correct answer is: B. output produced.

Piece workers are paid a certain amount for each unit of output they produce. This is in contrast to salaried workers, who are paid a fixed amount regardless of how much they produce. Piecework is often used in manufacturing and other industries where output can be easily measured.

Option A is incorrect because piece workers are paid based on the output they produce, not the output that is sold. Option C is incorrect because piece workers are paid based on the output they produce, not the output that is in stock. Option D is incorrect because piece workers are paid based on the output they produce, not the input they receive.