What would be an appropriate sample of invoices to gain reasonable assurance that all payments are properly authorised as part of the annual audit?

(a) Randomly pick one month and select every invoice for that month.

(b) Randomly select a sample of 100 invoices from throughout the financial year.

(c) Select all invoices greater than £5,000 generated throughout the year.

(d) Any of the above tests would be acceptable.

Choose the best answer.