The processes described above are steps in the purification and treatment of municipal wastewater. The steps are listed in random order. Which of the following lists the steps in the correct sequence?
a. Water is passed through a screen to remove debris.
b. Pathogenic organisms are killed by chlorination, UV, or ozone.
c. Suspended particles clump and settle out.
d. A floccing agent, such as alum, is added to the water.