Which of the Following Statements About Internal Audit's Follow-Up Process

Which of the following statements about internal audit's follow-up process is true?

A) The nature, timing, and extent of follow-up for assurance engagements is standardized to ensure quality performance.
B) The actions of external auditors and other external assurance providers is not encompassed by internal audit's follow-up process.
C) Internal auditors have responsibility for determining if management and the board have implemented the recommended action or otherwise accepted the risk.
D) The follow-up process must be complete and documented in the working papers in order to conclude the engagement.