What is the difference between $Cp$ and $Cpk?$

A$)$ Cp measures the capability of the process, while Cpk measures the variation in a process

B$)Cp$ measures the variation in a process, while Cpk measures the capability of the process

C$)$ Cp compares the voice of the process to the voice of the customer, while Cpk does not take into account the voice of the customer

D$)$ Cp measures the capability of the process, while Cpk measures the capability of the process taking into account if the process is centered