Identify each of the following statements as either a positive statement or a normative statement: 

a. Raising taxes on pollution emissions will result in some factories closing. 

b. The federal government should tax pollution to address climate change. 

c. An increase in the gasoline tax will reduce the amount that people drive and therefore cause a reduction in air pollution. 

d. If the federal income tax is increased, workers will decide to increase the number of hours they work each year.