Insert the missing word:

The level of . . . . . . . . . . . . . . . . . depends on the type of work and auditors employed. For more senior staff, this may be based mainly around the final review procedure, with little involvement from audit management during field work. For less senior staff, a lead auditor may be appointed or the audit manager may spend time with auditors on site. The amount of . . . . . . . . . . . . . . . . . . . . should correspond with the need to exercise close control over the project.

a. participation

b. motivation

c. performance appraisal

d. supervision