def statement_passive_verb(stmt_type):
    """Return the passive / state verb form of a statement type.

    Parameters
    ----------
    stmt_type : str
        The lower case string form of a statement type, for instance,
        'phosphorylation'.

    Returns
    -------
    str
        The passive/state verb form of a statement type, for instance,
        'phosphorylated'.
    """
    override = {'complex': 'bound', 'regulateamount': 'amount regulated',
        'decreaseamount': 'decreased', 'increaseamount': 'increased', 'gap':
        'GAP-regulated', 'gef': 'GEF-regulated', 'gtpactivation':
        'GTP-activated', 'influence': 'influenced', 'event': 'happened',
        'conversion': 'converted', 'modification': 'modified',
        'addmodification': 'modified', 'removemodification': 'unmodified',
        'regulateactivity': 'activity regulated'}
    return override.get(stmt_type) if stmt_type in override else stmt_type[:-3
        ] + 'ed'
