Consider a diagram containing isocost curves for the production of a given level of a final commodity in the household production model. Assume that purchased inputs are represented on the vertical axis while the time input is measured on the horizontal axis. A decrease in the wage rate will cause the isocost curves to:
A. become steeper.
B. become flatter.
C. remain unchanged.
D. become steeper or flatter depending on the magnitude of the wage increase.