A manufacturer of silk inspects each bolt of material at the end of the manufacturing process. When the process is in control, it averages $11$ defects per bolt. If a $2-$sigma control limit is used, what should be done if a bolt is found with $3$ defects?

Do nothing; the process is in control.

Do nothing even though the process is out of control.

Management should investigate and exploit the common causes of variation present.

Management should investigate and exploit the assignable causes of variation present.

None of the above answers are correct.