उत्सर्जन तन्त्र (Excretory System) का मुख्य अंग कौन सा है?

उत्तर: (B) वृक्क (Kidney) — Kidney (वृक्क) is the primary excretory organ — filters blood, removes urea/waste, produces urine. Each kidney has ~1 million nephrons. Other excretory organs: lungs (CO₂), skin (sweat), liver (bile)....