Consider the following statements as regards a Septic Tank:1. The size required is large and uneconomical when serving more than roughly 100 persons.2. It can remove around 90% of BOD and 80% of suspended solids.3. As compared to the sludge holding of a plain sedimentation tank, a septic tank can hold about 90% less of sludge volume.4. Frequent removal of sludge is not required.Which of the above statements are correct?

• A. 1 and 2
• B. 2 and 3
• C. 3 and 4
• D. 1 and 4