Which Is Correct? A Witness in a Civil Case Who Has Difficulty Remembering

Which is correct?
A witness in a civil case who has difficulty remembering the degree of detail needed to answer questions put to him may …

A) not refer to any document to assist him give the detail required.
B) refer to a document to assist him give the detail required provided the document was made at the time the events took place or soon afterwards and provided the document has already been produced to the other party and the court.
C) refer to a document provided it is in his witness statement and is endorsed with a statement of truth.
D) not refer to any document unless the permission of the court is sought and has been granted.