Concept:
This question focuses on bilateral and regional diplomacy in South Asia involving India, Pakistan, Bangladesh, and Afghanistan.
Step 1: Matching Water and Nuclear Milestones.
• A. Farakka Treaty (1996): The 30-year treaty for sharing the Ganges water at Farakka was signed between India (Prime Minister H.D. Deve Gowda) and Bangladesh (Prime Minister Sheikh Hasina) in December 1996. (A-IV)
• B. Pakistan Nuclear Tests (1998): Following India's Pokhran-II tests in May 1998, Pakistan conducted its own nuclear tests (Chagai-I and II) in late May 1998. (B-III)
Step 2: Matching Summits and Regional Expansion.
• C. Agra Summit (2001): This historic summit between Indian PM Atal Bihari Vajpayee and Pakistani President Pervez Musharraf took place in July 2001. Though it ended without a joint statement, it was a major diplomatic event. (C-II)
• D. Afghanistan joins SAARC (2007): Afghanistan became the 8th member of the South Asian Association for Regional Cooperation during the 14th summit held in New Delhi in 2007. (D-I)
Step 3: Final Sequence.
Mapping A-IV, B-III, C-II, D-I results in Option (4).