At the junction of which river basins are most of the Harappan sites…

The correct answer is Option (1) → Between the Indus and the Saraswati basin

So far more than 2000 Harappan sites have been discovered in the subcontinent, and most of them lie between the Indus and the Saraswati river basins. Nearly two-thirds of these settlements are in the Saraswati basin, which shows how important this river was for the civilisation. Among the Harappan sites, five major cities have been identified: Rakhigarhi, Mohenjodaro, Harappa, Dholavira and Ganweriwala.