ANS:D - all a, b & c.

Lowering the recrystallization temperature of metals can indeed be achieved by: a. Grain refinement: Smaller grain sizes lead to a larger number of grain boundaries, which act as barriers to the movement of dislocations during recrystallization. As a result, the recrystallization temperature is reduced. b. Purification: Impurities in metals can hinder the movement of dislocations and impede the process of recrystallization. By purifying the metal and reducing the concentration of impurities, the recrystallization temperature can be lowered. c. Working at lower temperature: Deforming the metal at lower temperatures (cold working) can introduce a higher density of dislocations. During subsequent annealing or heat treatment, these dislocations facilitate the initiation of recrystallization at lower temperatures compared to untreated or less cold worked metals. So, the correct answer is: all a, b & c.