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: Theresa went to the zoo for the first time. Sentence2: She visit the zoo with her younger sister and friends. Sentence3: Suddenly theresa noticed that her younger sister was out of her sight. Sentence4: They tried to find her sister each place as possible. Sentence5: Luckily,they found her at the corner watching the fishes.
Friends, Theresa, Younger sister