The internal auditor for a pharmaceutical manufacturer was reviewing the accounts receivable activities. The auditor ascertained that controls provided reasonable assurance that:
1. Sales are billed accurately and promptly. '
2. Accounts receivable ^re recorded properly.
3. Accounts receivable are aged and followed up to ensure prompt collections.
Required: 

For each of the three activities stated above, list three internal audit work steps to determine whether these activities are being carried out satisfactorily; that is, whether the controls are working as intended.