Quality control chart for averages was maintained for a dimension of the product. After the control was established, it was found that the standard deviation ($\sigma$) of the process was 1.00 mm. The dimension of the part is 70 ± 2.5 mm. Parts above 72.5 mm can be reworked but parts below 67.5 mm have to be scrappe(d) What should be the setting of the process to ensure production of no scrap and to minimize the rework?
(a) 68.5 mm (b) 70 mm
(c) 70.5 mm (d) 72.5 mm