Hi,
Answer: A) Sewage treatment plant
My work: Acid rain is a big pollution. Acid rain is caused by smoke in a rain cloud do to pollution from smock factories.This make A correct, because even if though Sewage treatment plants clean pollution they produce pollution from there plants.
Word you might not know:
1) Pollution - A harmful substance
2) Acid - Dissolve like substance
I Hope I Helped!
~KingJupiter