Which of the following statement best describes the understanding with respect to ownership and custody of working papers prepared by an auditor?

A. The working papers may be obtained by third parties when they appear to be relevant to issues raised in litigation
B. The safe custody of working papers is the responsibility of client, if kept at his premises
C. The working papers must be retained by an audit firm for a period of 10 years
D. Successor auditors may have access to working papers of the predecessor auditors. The approval of client is not required.