def choose_unit_from_multiple_time_units_series(time_serie, time_key="seconds"):
    """Given a time series in the form
        [(x,  {'hours': 0, 'seconds': 0, 'minutes': 0, 'days': 0}),
         (y,  {'hours': 0, 'seconds': 0, 'minutes': 0, 'days': 0}),
         (z,  {'hours': 0, 'seconds': 0, 'minutes': 0, 'days': 0})
        ]
    
    and an a time key like: minutes, hours, days, seconds
    return
        [(x, num), (y, num), (z, num)]
    """
    return  [tuple((pair[0], pair[1][time_key])) for pair in time_serie]