Explanation
Creating a single Attribute Group that links Customers to Contacts, Orders to Customers, and Products to Orders is the best way to facilitate this within Contact Builder. This way, NTO can create a single data model that connects all the relevant data extensions and allows accessing customer data across different attributes.
Creating three distinct Attribute Groups that link each data extension directly to Contacts is not correct, as it does not establish the relationships between Customers, Orders, and Products. Creating three distinct Attribute Groups that link Customers to Contacts, Orders to Customers, and Products to Orders is not correct, as it creates unnecessary duplication of data models. Creating a single Attribute Group that links Contacts to Customers, Orders to Products, and Products to Customers is not correct, as it does not reflect the logical hierarchy of the data extensions.