TASK DEFINITION: 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.
PROBLEM: Sentence1: Bret went mountain climbing in Alaska. Sentence2: He was near the summit of the mountain when a storm struck. Sentence3: Bret had to build a snow cave to keep warm. Sentence4: Bret survived the storm that lasted two days. Sentence5: Bret was glad that he knew mountain survival techniques.

SOLUTION: Bret

PROBLEM: Sentence1: Tony went to the park to see friends. Sentence2: They found an open field to play in. Sentence3: They all played soccer and Tony was the goalie. Sentence4: Tony made a big save to help his team win. Sentence5: All his friends cheered Tony for his great save.

SOLUTION: Tony, Friends

PROBLEM: Sentence1: Joan was invited to the Smiths' for dinner. Sentence2: She brought an expensive bottle of wine to impress them. Sentence3: David Smith drank most of it and became rather violent. Sentence4: Mary Smith explained that her husband was a recovering alcoholic. Sentence5: Joan vowed never to visit with them again.

SOLUTION:
Joan, Mary smith, David