BD
use trigger to populate denormalized fields

B. Use triggers to populate denormalized related fields on the Account.

By using triggers to create denormalized fields on the Account object, you can store relevant information from contacts, opportunities, and orders directly on the Account records. This approach reduces the complexity of report queries and can significantly improve report performance, especially in a large data volume environment.

D. Use an indexed field with bounded date filters.

Leveraging indexed fields in Salesforce can significantly improve query and report performance. Using bounded date filters (such as filtering for Accounts opened in the past year) ensures that the report query is more efficient by scanning a smaller subset of data.
Reports running on millions of records can become slow or time out. Using indexed fields and bounded filters helps in narrowing down the data set, leading to faster report generation.