Internal auditors frequently use the audit technique of observation. Which of the following statements best reflects the auditor's view of observation?

a. It should be performed separately from any other audit fieldwork function.

b. It is essentially related to the review of work flow and plant layout.

c. It is generally considered to be less authentic evidence than copies of basic documents describing the control process.

d. It can be supported by photography, flowcharts, drawings, and narrative.

e. All of the above.