The suggested answer is B.
To meet the requirements of scaling easily, handling transactions with minimal latency, providing a reliable customer experience, and retaining a relational schema, the best choice is to deploy Cloud Spanner using a multi-region instance. Cloud Spanner is a globally distributed, horizontally scalable, and strongly consistent database service designed for relational data. By deploying it with a multi-region instance and placing compute resources close to the default leader region, you ensure low latency and high availability for global operations, making it ideal for a large retail and ecommerce company's needs.