The UCL and LCL for an 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$?$

Nothing; the process is in control.

Explore the assignable causes because the second, fourth, and fifth samples are above the mean.

Explore the assignable causes because there is a run.

Explore the assignable causes because there is a trend.