A process control chart:

Select one:

a$.$

Assumes that $99\mathrm{.}74\%$ of special cause variation will fall between upper and lower limits

b$.$

Has upper and lower control limits set at $\backslash$pm $2$ standard deviations from the center line

c$.$

Separates the assignable cause of variation from the common cause of variation

d$.$

Assigns causes of variation to operator, machine, or material