Arrange the steps of municipal waste water treatment in a correct sequence:

(a) Grit is removed by sedimentation 

(b) Removal of floating debris by sequential filtration

(c) Digestion of aerobic bacteria and fungi in sludge by anaerobic bacteria.

(d) Vigorous growth of useful aerobic microbes into flocs

• A

  (a), (b), (d), (c)

• B

  (b), (a), (c), (d)

• C

  (b), (a), (d), (c)

• D

  (d), (c), (b), (a)