The correct option is A Digester - Anaerobic respiration
The functions of various component of a biogas plant are as follows:
1. Mixing Tank - mixes cow dung and water to form slurry
2. Inlet Chamber - sends slurry into the digester chamber
3. Digester Tank - fermentation by anaerobic bacteria
4. Outlet Chamber - the chamber through which manure which is formed after the fermentation is removed
5. Overflow Tank - Extra slurry is collected in the overflow tank
6. Dome Shaped Gas Holder - collects the biogas produced.
7. Gas Outlet - controls gas flow out of the gas chamber