Which of the following statements correctly defines Cp and Cpk?

A. Cp is considered to be "short-term capability", while Cpk is the "long-term capability".

B. Cp and Cpk are both measures of process efficiency and can be used interchangeably.

C. Cp measures the proportion of defects in a process, while Cpk measures the process capability.

D. Cp represents the potential capability of a process if it were centered at a target value, while Cpk represents the actual capability of the process.

E. Cp represents the actual capability of a process, while Cpk represents the potential capability of a process if it were centered at a target value.