• Rotary vs. Sickle Bar Mowers:
• Assertion (A): The power requirement of a rotary mower is much higher than that of a sickle bar mower of the same width. $\implies$ True.
• Rotary mowers cut by high-velocity impact without a ledger plate, operating at blade tip speeds of 70–80 m/s, incurring high aerodynamic windage and impact energy losses (3–5 times more power than sickle bar mowers).
• Reason (R): The knives of rotary mower are hinged to the disc or drum so that they can swing back if they hit a rock or other obstruction; centrifugal force keeps the knives in cutting position during normal operation. $\implies$ True.
• Rotary mower knives are freely pivoted for obstacle safety.
• Relationship: Reason (R) describes a safety mechanism for obstacle evasion, not the physical cause of high power consumption (which stems from aerodynamic drag and high-velocity impact).
• Conclusion: Both (A) and (R) are true but (R) is NOT the correct explanation of (A) (Option 2).

Correct option: (2) Both (A) and (R) are true but (R) is NOT the correct explanation of (A).

• Secondary (Biological) Wastewater Treatment Processes:
• Secondary wastewater treatment targets dissolved and colloidal biodegradable organic matter using biological cultures:
• Anaerobic lagoons: Earthen deep ponds utilizing anaerobic bacterial digestion for high-strength organic wastes.
• Trickling filters: Fixed-film aerobic biological reactors where wastewater trickles over rocky/plastic media coated with microbial slime.
• Activated sludge process: Suspended-growth aerobic bioreactor with continuous sludge recycling.
• (A) Sedimentation (primary clarifier) is a primary physical treatment method, not a biological secondary treatment process.
• Conclusion: (B), (C) and (D) only (Option 4).

Correct option: (4) (B), (C) and (D) only.