Concept:
This question examines two distinct issues in India-Pakistan relations: water sharing and territorial disputes.
Step 1: Evaluating Assertion (A).
Assertion (A) is correct in its substance but technically contains a common historical nuance. In 1960, India and Pakistan signed the Indus Waters Treaty to distribute the waters of the Indus river system. While the World Bank (then the IBRD) was the primary mediator and facilitator of the treaty, the assertion correctly identifies that the treaty was signed in 1960 and involved international institutional help.
Step 2: Evaluating Reason (R).
Reason (R) is also correct. Sir Creek is a 96-km long strip of water in the Rann of Kutch marshlands. India and Pakistan disagree on the interpretation of the boundary line (whether it should follow the center of the navigable channel or the eastern bank). This dispute remains unresolved.
Step 3: Analyzing the Relationship.
Although both statements are factually correct, the Reason (R) does not explain the Assertion (A). The Sir Creek dispute is a maritime/territorial boundary issue, while the Indus Waters Treaty is a water-sharing agreement. One is not the cause or explanation of the other; they are independent issues within the larger bilateral conflict.