Answer:
The correct answer is
d. Sampling Interval = Population size ÷ Sample size.
Step-by-step explanation:
According to Johnstone et al., (2014) "Once the auditor has determined the appropriate sample size, a sampling interval is calculated by dividing the population size by the sample size."
Thus,
Sampling Interval = Population size ÷ Sample size.
Johnstone, K., Rittenberg, L. and Gramling, A. (2014). Auditing: A Risk-Based Approach to Conducting a Quality Audit. Ninth Edition.