Which of the Following Exemplifies Voluntary Turnover

Which of the following exemplifies voluntary turnover?

A) Jake a student intern at CL Corp. leaves the organization after his internship period is over.
B) Paul, an employee of NML Corp. for five years, was fired owing to noncompliance with company policies.
C) Karen is asked to resign by her manager due to her deteriorating performance.
D) Gerald gets passed over for promotion twice despite being good at his job, and hence he decides to leave the organization.