Answer: Prey on pests like aphids and mosquitoes.
- A Fix atmospheric nitrogen in the soil
- B Prey on pests like aphids and mosquitoes
- C Decompose crop residues
- D Pollinate the flowers
Correct answer: B. Prey on pests like aphids and mosquitoes
Explanation: Ladybirds are useful in getting rid of aphids and dragonflies control mosquitoes, so they serve as biological controls for these pests.
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