Which of the following are possible advantages of using bacteria in sewage treatment? (i) Bacteria multiply quickly, thus producing a cheap and abundant source of enzymes. (ii) Only one type of bacteria is required to provide the various enzymes necessary for different kinds of wastes. (iii) Bacteria can break down waste under anaerobic or aerobic condition.

• A. (i) only
• B. (i) and (iii) only
• C. (ii) and (iii) only
• D. (i), (ii) and (iii)