If the-depletion of the oxygen is found to be 3 mg/litre after incubating 5 ml of sewage diluted to 250 ml for 5 days at $$20^\circ  C$$ B.O.D of the sewage is

A

150 mg/litre

B

250 mg/litre

C

350 mg/litre

D

400 mg/litre