The correct answer is (d) Jointing stage.
The jointing stage is the most critical stage of irrigation in wheat because it is the stage when the plant is forming its tillers. Tillers are the secondary stems that grow from the main stem of the plant. The more tillers a plant has, the more grain it will produce. If the plant does not receive enough water during the jointing stage, it will not produce as many tillers and will therefore produce less grain.
The C.R.I. state (Critical Reproductive Initiation) is the stage when the plant is beginning to flower. The late tilting stage is the stage when the plant is beginning to form its head. The boot stage is the stage when the plant is beginning to form its grain.
All of these stages are important, but the jointing stage is the most critical because it is the stage when the plant is forming its tillers.