Coal mines drainage waste water (acidic in nature) results from the earth's water percolating through the voids created in coal bed during mining. This polluted water which either drains out naturally to water courses or are removed before starting the mining is

• A. None of these
• B. Diluted with fresh water to reduce its acidity
• C. Left as such without any treatment
• D. Neutralised by alkali treatment

Answer: (D)