The Phillips curve depicts the relationship between the a. unemployment rate and the change in GDP. b. inflation rate and the interest rate. c. level of investment spending and the interest rate. d. inflation rate and the unemployment rate.

The Phillips curve is a concept in economics that shows the relationship between inflation and unemployment. It suggests an inverse relationship between the two, meaning that higher inflation is associated with lower unemployment and vice versa. The Phillips curve is usually presented as a downward-sloping curve on a graph with inflation on the y-axis and unemployment on the x-axis.

Let's analyze each of the options and find the one that correctly describes the Phillips curve: a. The unemployment rate and the change in GDP: This option does not describe the Phillips curve, as the Phillips curve relates to inflation and unemployment, not GDP. b. The inflation rate and the interest rate: This option does not describe the Phillips curve, as it relates the inflation rate to the interest rate, not unemployment. c. The level of investment spending and the interest rate: This option does not describe the Phillips curve, as it relates investment spending to the interest rate, not inflation and unemployment. d. The inflation rate and the unemployment rate: This option correctly describes the Phillips curve, as it shows the relationship between the inflation rate and the unemployment rate. Based on this analysis, the correct option is:

The Phillips curve depicts the relationship between the inflation rate and the unemployment rate. Therefore, the correct answer is option (d).