Consider the following statements regarding contact stabilization process:1. Primary settling tank is not required in some cases.2. BOD removal occurs in two stages.3. Aeration volume requirements are approximately 50% of those of a conventional – or tapered – aeration plant.4. Returned sludge is aerated for 30 min to 90 min in sludge aeration tank.Which of the above statements are correct?

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