def quantity_string(name, quantity_dict):
    """Takes in an abbreviation for a quantity and a quantity dictionary,
       and returns a more descriptive string of the quantity as "name (units)."
       Raises ValueError if the name is not in quantity_dict
    """
    if name not in quantity_dict.keys():
        raise ValueError('{0} is not present in quantity_dict'.format(name))
    return '{0} ({1})'.format(quantity_dict[name]['name'], quantity_dict[
        name]['units'])
