Quality Control Charts Usually Have a Central Line and Upper

Multiple Choice

Quality control charts usually have a central line and upper and lower control limit lines.Which of the following is a reason that the process being monitored with the chart should be investigated?

A) A single plot falls above or below the control limits.
B) Behavior is normal.
C) A large number of plots are on or near the central line.
D) There is no real trend in any direction.
E) There is a change in raw materials or operators.