ANS:D - forging and turning to size.

Large diameter shafts are typically manufactured by forging and then turned to size. Forging involves shaping metal using compressive forces, typically applied with a hammer or a press. Forging is well-suited for producing large and heavy components like shafts because it allows for the consolidation of the material and the alignment of the grain structure, resulting in improved mechanical properties such as strength and fatigue resistance. After forging, the shaft is turned to its final dimensions and surface finish. Turning is a machining operation performed on a lathe, where the workpiece (the forged shaft in this case) is rotated while a cutting tool removes material to achieve the desired size and shape. Therefore, the correct option is: forging and turning to size.