All of Grayson's stock was stolen when his business was burgled on 4 March 2004. His stock at 31 December 2003 was $23 000. From 1 January to 4 March 2004 sales totalled $42 000 and purchases were $38 000. Grayson's mark-up on goods is 33 1/3% to arrive at selling price. 

What was the cost of the stock that was stolen? 

A. $28 000 

B. $29 500 

C. $33 000 

D. $40 000