For the month of April, budgeted sales were $100,000 and budgeted cost of goods sold was $80,000. Actual sales were $80,000 and actual cost of goods sold amounted to $90,000. In preparing its monthly performance report:

A. an unfavorable cost variance of $20,000. B. a favorable cost variance of $20,000. C. a favorable cost variance of $10,000. D. an unfavorable cost variance of $10,000. E. None of these.