Which of the Following Is an Example of Before and After

Multiple Choice

Which of the following is an example of before and after comparisons?

A) The estimation of the quantity demanded of a good when its price is $5
B) The estimation of the demand for a particular good when consumer income is $10
C) The estimation of the ideal number of workers a firm should hire when wage rate is $20 per hour
D) The estimation of the supply of a good when the wage rate of labor changes from $30 to $10 per hour