An example of an external source document is ... : Select one:a.duplicate bank deposit slipsb.duplicate receiptsc.signed credit card slipsd.original receipts

To determine which option is an external source document, we should analyze each choice:

1. Duplicate Bank Deposit Slips: These are usually internal documents since they are copies made for internal record-keeping after a transaction has occurred.

2. Duplicate Receipts: Similar to deposit slips, duplicate receipts are typically internal documents that serve as a record for transactions made within the business.

3. Signed Credit Card Slips: These slips are usually generated at the point of sale and serve as proof of a transaction. While they can be used as records by the business, they are often also considered external documents as they are generated by the credit card processing company and involve an external transaction.

4. Original Receipts: These documents are typically proof of purchase and serve as internal records, but they can be issued by external vendors. They are often used by businesses to verify expenses that have been incurred outside the organization.

Conclusion

The best option that represents an external source document, as it relates to transactions with external parties, would be c. signed credit card slips.