Which of the Following Statements Are True

Which of the following statements are true?

A) We might think of "natural random variation" as uncontrollable background noise.
B) Control charts provide a mechanism for recognizing situations where assignable causes may be adversely affecting product quality.
C) Once a control chart indicates an out-of-control situation, an investigation can be launched to identify causes and take corrective action.
D) A basic element of control charting is that samples have been selected from the process of interest at a sequence of time points.
E) All of the above statements are true.