Final answer:
Adjusting entries must be performed at the end of an accounting period when accounts are ready to be closed.
Step-by-step explanation:
The activity that must be performed at the end of an accounting period when accounts are ready to be closed is a) Adjusting entries. Adjusting entries are made to update the accounts and reflect any transactions or events that have occurred during the period but have not yet been recorded. These entries ensure that the financial statements accurately represent the financial position and operating results of the company.