365. Consider the following statements regarding double filtration.1. The rate of filtration of slow sand filters can be considerably increased by using a roughening filter2. The raw water is first of all passed through slow sand filters3. The roughening filter is rapid gravity filter in which finer sands is used compared to ordinary rapid gravity filters.4. The roughening filter reduces the loadon the slow sand filter and thus increases the filtration rate. Of these statements:
A. 1 and 2 are correct
B. 2 and 3 are correct
C. 3 and 4 are correct
D. 2 and 3 are correct

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