Answer: B. decreases aggregate supply because firms' costs increase
Step-by-step explanation:
The rise in the the minimum wage rate raise the production cost .
This tends to shift the aggregate supply curve leftwards because the profit margins of firm will decrease and that tends to decrease the production.( at each unite of production.)
Hence, the rise in the minimum wage decreases aggregate supply because firms' costs increase .
Therefore , the correct option is 'B'.