The following units of a particular item were available for sale during the period: Beginning inventory First purchase Second purchase Third purchase 40 units at $20 50 units at $21 50 units at $22 50 units at $23 What is the unit cost of the 35 units on hand at the end of the period as determined under the periodic inventory system by the fifo costing method?  LO1A. $20 B. $21 C. $22 D. $23