Consider the following assertion: In the Pleistocene period either the Yamuna once flowed into the Indus, or the Sutlej flowed into the Yamuna and one major tributary of either had shifted from the Ganga to the Indus or vice versa. Which of the following is/are the basis of the above assertion? 1. The Nadi-Sukta of the Rigveda 2. The explorations of the Sutlej and the Yamuna by Robert Bruce Foote 3. The presence of the same species of dolphins in both the Indus and the Ganga river systems

The assertion is about a geological/palaeo-hydrological event in the Pleistocene linking the Indus and Ganga drainage systems. The most compelling modern scientific evidence for such a river capture/exchange is biogeographical — namely, the presence of the same species of freshwater dolphin (Platanista gangetica) in both the Indus and Ganga river systems, which can only be explained if the two systems were once connected. The Rigveda's Nadi-Sukta relates to Vedic-era river identification, not Pleistocene geology, and Robert Bruce Foote's explorations were primarily palaeolithic archaeological surveys, not specifically focused on Sutlej-Yamuna palaeo-channels in this hypothesis. Hence only 3 is the basis.