The correct answer is: A. quantity of work done.
Under piece rate system of wage payment, workers are paid a fixed amount for each unit of work they produce. This system is often used in manufacturing and other industries where output can be easily measured. Piece rate systems can be effective in motivating workers to produce more, but they can also lead to quality problems if workers are not careful.
Option B is incorrect because under piece rate system, workers are not paid for the time they spend working, but for the number of units they produce.
Option C is incorrect because under piece rate system, workers are paid for the quantity of work done, not for both the quantity and time.
Option D is incorrect because under piece rate system, workers are paid for the quantity of work done.