I’m trying to study for an exam but I can’t figure out the diffrence between a parallel structure and a non parallel structure can someone give me examples pls and a detailed explanation on why it is or not parallel?

Choose the sentence that is not logically connected in the paragraph. (1) doctor henderson was a kind and gentle man. (2) his patients loved and respected him. his death made many of them sad. (3) as a young man, he decided to become a doctor and pursue a life of healing and comforting. (4) his work will long be remembered by the citizens of battle creek, michigan.