Which Is Not a Rule of Thumb to Indicate an Out-Of-Control

Multiple Choice

Which is not a rule of thumb to indicate an out-of-control process on the $\overline { X ^ { * } }$ chart?

A) Single point outside three sigma
B) Three of four successive points outside two sigma on the same side of the centerline
C) Four of five successive points outside one sigma on the same side of the centerline
D) Nine successive points on the same side of the centerline