Which of the following best explains the difference between a Control Limit and a Spec Limit?

Question $51$ options:

a$)$

There should be no difference between a Spec Limit and Control Limit

b$)$

None of the above are true

c$)$

Spec Limits come from the customer and Control Limits are calculated using the mean and standard deviation from process data

d$)$

Control Limits come from the customer and Spec Limits are calculated using the mean and standard deviation from process data