Which of the following situations does not indicate that a process being monitored with a control chart should be investigated to see if the process is out of control?

a. Two or more consecutive plots are close to the upper limit of the control chart.

b. A run of five or more consecutive plots are above the center line of the control chart.

c. A series of consecutive plots are evenly distributed close to the center line of the control chart.

d. A series of five or more consecutive plots exhibits an increasing trend towards the upper limit of the control chart.

e. A single plot falls below the lower limit of the control chart.