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

• A.  Uplift of folded Himalayan series
• B.  Syntaxial bending of geologically young Himalayas
• C.  Geo-tectonic disturbance in the tertiary folded mountain chains
• D.  Both [a] and [b]