Which of the Following Statements Is True Regarding Assurance Services

Which of the following statements is true regarding assurance services provided to clients outside of the organization?

A) Assurance services for outside clients are not covered under the internal audit charter.
B) Assurance services for outside clients must be approved on a case-by-case basis by the board of directors.
C) The nature of assurance services for outside clients should be defined in the internal audit charter.
D) The nature of assurance services for outside clients is the same as for internal clients.