A. encabezamiento.
In this question we must the Word which fits best to the Context and explain the Reason of selecting the choice.
In the situation described on statement we are suggested on how to write an Envelope correctly in order to guarantee that a document shall be sent to its Recipient. In this case, the word that fits best to the Context is the Spanish word encabezamiento (headline).
Hence, the correct answer is A.
Please see this related question in Spanish: https://brainly.com/question/19933101
