A. Create a report combining data from the Account standard object and the Invoices external object.
Salesforce allows for the creation of reports that include data from both standard objects and external objects, assuming the external data is accessible via Salesforce Connect. This approach enables users to view integrated data from Accounts and Invoices within a single Salesforce report, providing a unified view of customer and financial data. This is a straightforward solution that leverages Salesforce's reporting capabilities to meet the requirement without the need for custom development or external reporting tools.

C. Create a Visualforce page combining Salesforce Account data and Invoice external object data.
If the reporting requirements are complex and cannot be fully addressed by standard Salesforce reporting capabilities, especially when combining data from standard and external objects, a custom Visualforce page can be developed. This approach offers greater flexibility in how data is displayed and allows for the incorporation of complex logic or custom user interfaces that go beyond the capabilities of standard reports. Visualforce pages can query both Salesforce data and external object data, enabling the creation of highly customized reports that meet specific business needs....