Mean $$ \pm\, 3\sigma $$ covers-

The correct answer is $\boxed{\text{C}}$.

The 68-95-99.7 rule, also known as the empirical rule or the three-sigma rule, is a common rule of thumb in statistics that states that approximately 68% of the values in a normally distributed population will lie within 1 standard deviation (σ) of the mean, approximately 95% of the values will lie within 2 standard deviations (2σ) of the mean, and approximately 99.7% of the values will lie within 3 standard deviations (3σ) of the mean.

Therefore, the mean $\pm\, 3\sigma$ covers 99.7% of the items.