* A:Using the order number as an external ID ensures Salesforce can identify and update existing records instead of creating duplicates during updates.
* B:Ensuring the order number is unique in the OMS guarantees that there will not be multiple records in Salesforce corresponding to a single order.
Reference:External IDs in Salesforce
Incorrect Options:
C:Email on the contact is unrelated to the uniqueness of order records.
D:Deleting duplicates with triggers is reactive and not a best practice.