Choice "D" is correct. Quality control standards relate to the conduct of a firm's audit practice as a whole, and compliance with such standards would not be demonstrated by audit documentation for one specific audit engagement.
Choice "a" is incorrect. Audit documentation should clearly indicate the work performed and the evidence obtained.
Choice "b" is incorrect. Audit documentation should indicate which parties performed and reviewed the work.
Choice "c" is incorrect. Audit documentation should demonstrate compliance with the standards of fieldwork. It should indicate an appropriate level of planning and supervision, that a sufficient understanding of the entity and its environment, including its internal control, was obtained, and that a sufficient level of appropriate evidence was obtained.