Correct option is C
The cleaning period for a slow sand filter typically falls within one month to three months. Slow sand filters are designed to operate for extended periods before requiring cleaning, but the frequency can vary based on the water quality and filter usage.
5 to 10 days: Too short for slow sand filters.
Three months to six months: Generally a bit longer than the typical cleaning interval.
One month to three months: Correct, as this is the typical range for cleaning slow sand filters.
Two weeks to three weeks: Too short for slow sand filters.
Therefore, the correct answer is (c) One month to three months.
