A design engineer wants to construct a sample mean chart for controlling the service life of a halogen headlamp his company produces. On three recent production batches, he tested service Ite on random samples of four headlamps, with these results: Service Life (hours) 2 3 4 500 505 500 Sample 1 495 Sample 2 525 515 505 515 Sample 3 470 480 460 470 if the engineer uses upper and lower control limits of 520 and 480 hours, on what sample(s) (if any) does service life appear to be out of control? Select one: O a sample 1 b. all samples are in control c. sample 2 Od sample 3 O e both samples 2 and 3