The Brahmaputra, Irrawady and Mekong rivers originate in Tibet and flow it through narrow and parallel mountain ranges in their upper reaches. Of these riviers, Brahmaputra makes a "U" turn in its course to flow into india. This "U" turn is due to

• Uplift of folded Himalayan series
• Syntaxial bending of geologically young Himalayas
• Geo-tectonic disturbance in the tertiary folded mountain chains
• Both A and B