What fields are used as unique ID for CRM records?  

For example I have an Excel spreadsheet with this information/fields:

Company   First   Last   Email    LeadStatus    Phone   Notes/Comments   Temperature   Sales$$  #Emp  Website


Should this information first be imported into Leads?  Or should the Excel data be broken up with matching unique ID and imported separately into Leads, Accounts, Contacts separately using the unique ID to relate the records?  What does ZOHO CRM use to unique ID key.

Thank you.
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