A six sigma quality level:

a$)$ Implies $99\mathrm{.}73\%$ quality in products delivered to the customer

b$)$ Is the same as a Cp $=1\mathrm{.}33$

c$)$ Represents $3\mathrm{.}4$ defects per million opportunities

d$)$ Results in half the amount of defects compared to a $3$ sigma level