def word_for_char(X, character):
    """
    Diagnostic function, collect the words where a character appears
    :param X: a data matrix: a list wrapping a list of strings, with each sublist being a sentence.
    :param character:
    :return:
    >>> word_for_char( [['the', 'quick', 'brown'],['how', 'now', 'cow']], 'n')
    ['brown', 'now']
    """
    return [word
            for sentence in X
            for word in sentence
            if character in word]