The UCL and LCL for An $\bar { X } -$

Multiple Choice

The UCL and LCL for an $\bar { X } -$ chart are 25 and 15 respectively. The central line is 20, and the process variability is considered to be in statistical control. The results of the next six sample means are 18, 23, 17, 21, 24, and 16. What should you do?

A) Explore the assignable causes because there is a trend.
B) Nothing; the process is in control.
C) Explore the assignable causes because there is a run.
D) Explore the assignable causes because the second and fifth samples are above the mean.