On January 1, Mason sold 5,000 stereo systems for $3,000 each (cost $1,800). The stereo systems included an assurance-type warranty for the first year, and are estimated to cost $350 each. Mason also sold 2,000 optional extended coverage plans under which it will repair or replace any defective part for 2 years beyond the expiration of the assurance-type warranty. Determine each of the following as of December 31:

A. Sales Revenue

B. Unearned Revenue

C. Warranty liability

D. Warranty expense