estaban contestando
-they/you were answering
Imperfecto progresivo para el sujeto ellos/ellas/ustedes del verbo contestar.

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Primeramente, la intención era que las cartas fueran a diferentes personas, con distintos niveles de conciencia; segundo, en la mayoría de los casos las cartas estaban contestando ciertas preguntas y no eran escritos independientes.
Firstly, the letters were meant for several persons, at various stages of consciousness; secondly, in most cases they were answering certain questions and were not independent treatises.
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