Describe a process performing at $6-$sigma

Statistically in control with the mean $6$ standard deviations away from the nearest control limit$,$ produces $3\mathrm{.}4$

defects per opportunity.

None of these

Statistically in control with the mean $6$ standard deviations away from the nearest specification limit$,$

produces $3\mathrm{.}4$ defect per billion opportunities.

Statistically in control with the mean $6$ standard deviations away from the nearest specification limit$,$

produces $3\mathrm{.}4$ defects per million opportunities.