For which storage accounts can you implement the planned changes for storage?

The correct choice is storage1 only.

For Azure SQL Database auditing, Microsoft supports writing audit logs to an Azure Storage account. Both Standard storage accounts and Premium BlockBlobStorage accounts are supported as audit destinations. However, the question specifically requires configuring auditing for sql1 by using the Azure portal. Microsoft states that when auditing is configured through the Azure portal, the selected storage account must be in the same Azure region as the logical SQL server/database. Microsoft Learn

In this case, sql1 is located in West US. Of the available storage accounts, storage1 is also in West US and uses Standard performance, which is supported for SQL audit storage. Therefore, storage1 satisfies both the storage-type and regional requirements.

Although storage2 uses Premium Block blobs, which is technically supported for SQL auditing, it is located in East US, so it cannot be selected through the Azure portal for sql1. storage3 is Premium File shares and storage4 is Premium Page blobs; these are not supported SQL auditing storage destinations. Microsoft specifically identifies Standard storage and Premium BlockBlobStorage as supported.