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.