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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def load_source_vocabs(folder: str) -> List[Vocab]: """ Loads source vocabularies from folder. The first element in the list is the primary source vocabulary. Other elements correspond to optional additional source factor vocabularies found in folder. :param folder: Source folder. :return: List of vocabularies. """

    return [vocab_from_json(os.path.join(folder, fname)) for fname in
            sorted([f for f in os.listdir(folder) if f.startswith(C.VOCAB_SRC_PREFIX)])]