The text boxes in the left panel have been placed in a random order. Restore the original order by dragging the text boxes from the left panel to the right panel.
d) These harmful materials are called pollutants.
b) Pollutants can be natural, such as volcanic ash.
a) Pollution is the introduction of harmful materials into the environment.
c) They can also be created by human activity, such as trash or runoff produced by factories.