def drop_enclitics(X):
    """

    :param X: a data matrix: a list wrapping a list of strings, with each sublist being a sentence.
    :return: The matrix cleaned of enclitics
    >>> drop_enclitics([['arma', 'virum', '-que', 'cano']])
    [['arma', 'virum', 'cano']]
    """
    return [[word
             for word in sentence
             if not word.startswith('-')]
            for sentence in X]