Choice "D" is correct. The auditor is required to establish an understanding with the client, and this understanding should be documented in the form of an engagement letter. The understanding (and therefore the letter) should encompass management's responsibilities, which include providing the auditor with a representation letter at the conclusion of the engagement.
Choices "b", "c", and "a" are incorrect. An understanding generally is not obtained with respect to specific audit procedures, and therefore these items would not be included in an engagement letter.
