def filter_center_line(center_line):
    """Filter center line marks by the number of points they contain to find road
    marks that form the center line.

    Args:
        center_line (list): list of center line marks.

    Returns:
        A list of filtered center line marks.
    """
    filtered_center_line = []
    for road_mark in center_line:
        if road_mark.size > 70 or road_mark.size < 30:
            continue
        filtered_center_line.append(road_mark)
    return filtered_center_line
