In this task, you're given a story (which contains five sentences only). Your task is to find all the characters which are available in the given story.

Sentence1: Isaac was prone to bouts of depression. Sentence2: He never made many friends, and was usually found by himself. Sentence3: He imagined that no one would miss him and began to cry. Sentence4: His mother heard his sobbing and came to find out what was wrong. Sentence5: She encouraged him that she would miss him if he disappeared.
Isaac, Friends, Mother

Sentence1: Greta had noticed her son was having trouble focusing in school. Sentence2: Greta took her son to the doctor. Sentence3: The doctor diagnosed the boy with ADHD. Sentence4: The doctor prescribed medicine for him. Sentence5: Greta's son now focuses much better in class.
Greta, Greta's son, The doctor

Sentence1: Louisa was nervous to start her first day at a new school. Sentence2: As she entered the school building she felt uneasy. Sentence3: She was afraid she wouldn't make any friends. Sentence4: Thankfully a nice girl Tina reached out and invited her to lunch. Sentence5: Louisa was happy to make a new friend.
Louisa, Tina