Final answer:
In QuickBooks Online, the vendor list can be updated before entering transactions and while entering transactions. Therefore, the correct answer is: Before entering transactions and while entering transactions.
Step-by-step explanation:
In QuickBooks Online, the vendor list can be updated both before entering transactions and after entering transactions.
You can update the vendor list before entering transactions by going to the Vendor Center, selecting a vendor, and making changes to their information.
Additionally, you can also update the vendor list while entering transactions, by selecting a vendor and making necessary changes to their details right on the transaction form.
Therefore, the correct answer is: Before entering transactions and while entering transactions.