Answer: Legumes.
- A Paddy plants
- B Legumes
- C Wheat plants
- D Ferns
Correct answer: B. Legumes
Explanation: Rhizobium forms symbiotic associations with legumes, living in root nodules and fixing atmospheric nitrogen.
Sewage passes through physical removal (primary), then aerobic biological treatment where microbes form flocs that consume organic matter (secondary); the settled activated sludge is then digested anaerobically to produce biogas - a deliberate switch from aerobic to anaerobic conditions between stages.
Concept context
Microorganisms in food, medicine, sewage treatment, biocontrol, and biofertilizers