Insert the missing words:

The CAE should continuously seek out ways to improve the level of objectivity throughout audit and some of the relevant matters have been mentioned earlier. A great deal of this hinges on installing suitable . . . . . . . . . . . . . . . . . . . . , the aim being to remove any potential barriers.

a. staffing arrangements

b. whistleblowing procedures

c. policies and procedures

d. checks of audit work