MCQOPTIONS
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| 1. |
The period of cleaning of slow sand filter is usually: |
| A. | 30 days to 90 days |
| B. | 120 days to 180 days |
| C. | 90 days to 120 days |
| D. | 15 days to 30 days |
| Answer» B. 120 days to 180 days | |