The Rajasthan Canal is one of the most important irrigation systems in the state of Rajasthan. The canal construction began with the first phase in the district of Ganganagar. Ganganagar, located in the northern part of Rajasthan, is well-known for its agricultural importance, and the canal was a key project to support the region's farming community.
- Option (A) Jaisalmer is incorrect as it was not part of the first phase.
- Option (B) Barmer is also incorrect for the first phase.
- Option (C) Jodhpur is incorrect as well.
- Option (D) Ganganagar is the correct answer, as it was the district chosen for the first phase of the canal construction.
Thus, the correct answer is (D) Ganganagar.