Explanation
The student number is the external ID that the consultant should recommend to match spreadsheet information with the Salesforce Contact record. The external ID is a field that uniquely identifies a record and can be used to match records from different data sources. The student number is a unique identifier for each student that can be used to match the spreadsheet information with the Contact record in Salesforce. The email address, company name, and company phone are not unique identifiers for each student and cannot be used as external IDs. References:
https://help.salesforce.com/s/articleView?id=sf.data_loader_match_record.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.customize_externalid.htm&type=5