What is the purpose of statistical process control SPC$?$ A $)$ To monitor the process in order to know when the average number of defects is too high. B $)$ To keep quality records to show to customers $.$ C $)$ To monitor the process close enough that we know when the process has gone out $-$ of $-$ control $.$ D $)$ To monitor the process close enough that we know about quality problems before they happen $.$