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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def decode_cf_variables(variables, attributes, concat_characters=True, mask_and_scale=True, decode_times=True, decode_coords=True, drop_variables=None, use_cftime=None):
 """ Decode several CF encoded variables. See: decode_cf_variable """

    dimensions_used_by = defaultdict(list)
    for v in variables.values():
        for d in v.dims:
            dimensions_used_by[d].append(v)

    def stackable(dim):
        # figure out if a dimension can be concatenated over
        if dim in variables:
            return False
        for v in dimensions_used_by[dim]:
            if v.dtype.kind != 'S' or dim != v.dims[-1]:
                return False
        return True

    coord_names = set()

    if isinstance(drop_variables, str):
        drop_variables = [drop_variables]
    elif drop_variables is None:
        drop_variables = []
    drop_variables = set(drop_variables)

    # Time bounds coordinates might miss the decoding attributes
    if decode_times:
        _update_bounds_attributes(variables)

    new_vars = OrderedDict()
    for k, v in variables.items():
        if k in drop_variables:
            continue
        stack_char_dim = (concat_characters and v.dtype == 'S1' and
                          v.ndim > 0 and stackable(v.dims[-1]))
        new_vars[k] = decode_cf_variable(
            k, v, concat_characters=concat_characters,
            mask_and_scale=mask_and_scale, decode_times=decode_times,
            stack_char_dim=stack_char_dim, use_cftime=use_cftime)
        if decode_coords:
            var_attrs = new_vars[k].attrs
            if 'coordinates' in var_attrs:
                coord_str = var_attrs['coordinates']
                var_coord_names = coord_str.split()
                if all(k in variables for k in var_coord_names):
                    new_vars[k].encoding['coordinates'] = coord_str
                    del var_attrs['coordinates']
                    coord_names.update(var_coord_names)

    if decode_coords and 'coordinates' in attributes:
        attributes = OrderedDict(attributes)
        coord_names.update(attributes.pop('coordinates').split())

    return new_vars, attributes, coord_names