def add_ner_prompts(df, prompt_config, sep):
    """
    Combining sentences and entities to create prompts in Dataframe with 'sents' and 'entities' columns.
    Adds 'prompts' and 'empty_prompts' (prompt without answer) columns to DataFrame
    """

    prompts = []
    empty_prompts = []

    prompt_sample_structure = prompt_config['sent_intro'] + ' {}\n' + prompt_config['retrieval_message'] + ' {}'
    empty_prompt_sample_structure = prompt_config['sent_intro'] + ' {}\n' + prompt_config['retrieval_message']

    for i, row in df.iterrows():
        sent = row['sents']
        entities = sep.join(row['entities'])

        prompt = prompt_sample_structure.format(sent, entities)
        empty_prompt = empty_prompt_sample_structure.format(sent)

        prompts.append(prompt)
        empty_prompts.append(empty_prompt)

    df['prompts'] = prompts
    df['empty_prompts'] = empty_prompts

    return df