What should the developer do to ensure good data quality and to ensure that data imports, integrations, and searches perform well?

A developer needs to design a custom object that will be integrated into a back-end system.

What should the developer do to ensure good data quality and to ensure that data imports, integrations, and searches perform well? (Choose two.)
A . Configure a custom field as unique
B . Configure a custom field as indexed
C . Configure a custom field as external ID
D . Configure a custom field as Salesforce ID

Answer: A,C