Why is ApsaraDB for PolarDB better than other traditional database engines? (The number of answer 3)

A. When you purchase a PolarDB cluster, you don't need to specify the storage capacity you want to purchase

B. PolarDB supports both OLTP and OLAP scenarios very well

C. The PolarDB database engine won't require you to replicate data when adding read-only nodes

D. ApsaraDB for PolarDB uses the pay-as-you-go billing method, therefore you only need to pay for the storage resources you actually use