Which technique should the developer implement to streamline the data upload?

A primaryid_c custom field exists on the candidate_c custom object. The filed is used to store each candidate’s id number and is marked as Unique in the schema definition.

As part of a data enrichment process. Universal Containers has a CSV file that contains updated data for all candidates in the system, the file contains each Candidate’s primary id as a data point. Universal Containers wants to upload this information into Salesforce, while ensuring all data rows are correctly mapped to a candidate in the system.

Which technique should the developer implement to streamline the data upload?
A . Create a Process Builder on the Candidate_c object to map the records.
B . Create a before Insert trigger to correctly map the records.
C . Update the primaryid__c field definition to mark it as an External Id
D . Upload the CSV into a custom object related to Candidate_c.

Answer: C