Is “exercising is a good stress reliever.” a participle or gerund

Me which theme is developed by the changing relationship between the narrator and his daughter in this excerpt ? as she grew older, she spent more of her time with girls. so much time indeed did she spend with them that she came no more, as she used to do, to her father’s room. i was scarcely on speaking terms with her. when mini and her father stop communicating, it develops the theme that children should not speak unless spoken to. as mini becomes more independent, it develops the theme that parents must learn to let go as their children grow up. as mini spends more time with friends, it develops the theme that young people are more influenced by peers than by parents. when mini and her father see each other far less often, it develops the theme that absence makes the heart grow fonder.