You support a consumer inventory application that runs on a multi-region instance of Cloud Spanner. A customer opened a support ticket to complain about slow response times. You notice a Cloud Monitoring alert about high CPU utilization. You want to follow Google-recommended practices to address the CPU performance issue. What should you do first?

A. Increase the number of processing units. B. Modify the database schema, and add additional indexes. C. Shard data required by the application into multiple instances. D. Decrease the number of processing units.