def get_sentence_pair_with_placeholder(doc, idx):
    """
    Simply returns a placeholder in place of the second sentence (which would usually be randomly selected for the next sentence prediction task.
    """
    sent_1 = doc[idx]
    sent_2 = "_"

    label = False

    assert len(sent_1) > 0
    assert len(sent_2) > 0
    return sent_1, sent_2, label