What should the consultant recommend to ensure data integrity?

Cloud Kicks has an integration between the data warehouse and Salesforce. The VP of operations wants to synchronize customer data between the systems.

What should the consultant recommend to ensure data integrity?
A . Set up an External ID field on the Account object with Read only on the field security settings for all profiles except the admin profile.
B.Set up an import of the data from the data warehouse on a monthly basis using Data Loader.
C.Set up an encrypted field on the Account object with Read Only on the field security settings for all profiles except the admin profile.
D.5Set up a Process Builder process on the Account object to check for unique values on a monthly basis.

Answer: A