The $2.4$ ml of raw sewage is diluted to $240$ ml. The Dissolved Oxygen (DO) of the diluted sample at the beginning of Biochemical Oxygen Demand (BOD) test was $8 \mathrm{mg} / \mathrm{l}$ and it was $6 ~\mathrm{mg} / \mathrm{l}$ after $5$-day incubation at $20^{\circ} ~\mathrm{C}$.
The $\mathrm{BOD}_{5}$ (in $\mathrm{mg} / \mathrm{l}$ ) of the raw sewage is
- $200$
- $100$
- $250$
- $150$
