13. are the preferred communication channel when a confidential and formal record of a transaction is required for business conducted outside an organization.

The answer is "letters".

Explanation:

We call the letter name a type of message that takes the handwriting form that generates communication between people. The letter was created as a means of building contact between people who saw themselves spatially distant and who in times past without technological resources tried to communicate.

The privacy of a letter is and should always be protected by law. For this reason, the letter is the best option for communicating a confidential and formal record of a transaction.

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