The following units of a particular item were available for sale during the period:

Beginning inventory 40 units at $20

First purchase 50 units at $21

Second purchase 50 units at $22

Third purchase 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.

A. . $20

B. . $23

C. . $21

D. . $22