Bangladesh and Nepal have had differences over-

Himalayan waters

The correct answer is Option (3) → Himalayan waters

" Not all conflicts in South Asia are between India and its neighbours. Nepal and Bhutan, as well as Bangladesh and Myanmar, have had disagreements in the past over the migration of ethnic Nepalese into Bhutan and the Rohingyas from Myanmar into India and Bangladesh, respectively. Bangladesh and Nepal have had some differences over the future of the Himalayan river waters. The major conflicts and differences, though, are between India and the others, partly because of the geography of the region, in which India is located centrally and is therefore the only country that borders the others."