Concept:"Effluent" means liquid waste or discharge that flows out into a water body.
Explanation:In this sentence, "effluent" refers to waste material, especially liquid waste, that is poured into the stream from industrial or household sources.
Such discharge often contains pollutants, which makes the water unsafe for drinking.
Among the given choices, "sewage" is the nearest in meaning because it denotes the waste matter carried away by drains and sewers.
A disinfectant is a germ-killing chemical, oil is a greasy liquid, and a concoction is a prepared mixture.
None of these other options mean general liquid waste.
Therefore, the word closest in meaning to "effluent" in this context is sewage.
Answer:A. sewage