Choice "D" is correct. The auditor is not required to obtain knowledge about operating effectiveness as part of the understanding of internal control. This knowledge is obtained later, for specific controls on which the auditor plans to rely.
Choices "b", "a", and "c" are incorrect. During the planning phase of the audit, the auditor obtains an understanding of the internal control system by considering:

• The types of misstatements that may occur.

• The risk that misstatements may occur.

• Factors that influence the design of tests of controls and substantive tests.

• The assessment of inherent risk.

• Judgments about materiality.

• The complexity and sophistication of the entity's operations and systems.

• The use of manual vs. computerized control procedures.

Such knowledge may be obtained by appropriate inquiry, inspection, or observation. Knowledge may also be obtained based on previous experience with the client and/or an understanding of the industry in which the entity operates.