Suppose you are working for an auditing firm which utilizes a computer assisted audit/accounting tool (CAAT) such as ACL for analytical procedures. This tool has a function to detect duplicate observations of any specified attribute. You would use this "detect duplicates" function on which of the following attributes? 1) "Transaction amount" on the accounts receivables transaction file. 2) "Transaction ID" on the accounts receivables transaction file. 3) "Transaction date" on the accounts receivables transaction file. 4) "Customer ID" on the accounts receivables transaction file