What is the correct sequence of processes in a sewage treatment plant?

• A
  Sedimentation $\to$ Filtration $\to$ Aerobic bacteria $\to$ Anaerobic bacteria
• B
  Aerobic bacteria $\to$ Anaerobic bacteria $\to$ Sedimentation $\to$ Filtration
• C
  Filtration $\to$ Sedimentation $\to$ Aerobic bacteria $\to$ Anaerobic bacteria
• D
  Filtration $\to$ Anaerobic bacteria $\to$ Aerobic bacteria $\to$ Sedimentation