Choice "C" is correct. The extent of the auditor's consideration of the client's internal controls is affected by a variety of factors, with the primary goal being to obtain a sufficient understanding the entity and its environment, including its internal control. The amount of time budgeted to complete the audit should not be a primary factor in determining the extent of consideration of the client's internal controls--if more time is needed to adequately consider internal control, then the budget should be revised.
Choice "a" is incorrect. How frequently the control is performed would affect the extent of the auditor's consideration of the client's internal controls.
Choice "b" is incorrect. The expected deviation rate would affect the extent of the auditor's consideration of the client's internal controls.
Choice "d" is incorrect. The extent to which other tests provide evidence about the same assertion would affect the extent of the auditor's consideration of the client's internal controls.