The control charts based directly on the sample variance are called __

1.	The control charts based directly on the sample variance are called ____
A.	s Control charts
B.	‚âà√¨‚àö√¢<sup>2</sup> Control charts
C.	s<sup>2</sup> Control charts
D.	<span style="text-decoration:overline;">x</span> Charts
Answer» D. <span style="text-decoration:overline;">x</span> Charts

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