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.
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Question: Sentence1: My science class took a field trip to the bio park today. Sentence2: Only about half of the students were allowed to go on the trip. Sentence3: My best friend Mark got left behind because he failed a math test. Sentence4: That doesn't seem fair to me because he is really good at science. Sentence5: I don't understand why teachers punish students who really try hard.

Answer: Students, I (myself), Teachers, Mark

Question: Sentence1: Fred was a worker on his uncle's dock at the pier. Sentence2: He would work everyday cleaning, and catching fish. Sentence3: One day, he noticed a rather large fish in his nets. Sentence4: When he looked a second time, he realized the fish was a dolphin. Sentence5: Fred worked quickly to free the fish from the nets and release him.

Answer: Uncle, Dolphin, Fred

Question: Sentence1: Rick had a job as a traveling salesman. Sentence2: It required him to be gone from home often. Sentence3: He did not enjoy being away from his family. Sentence4: Rick tried to find a new job. Sentence5: He found one but had to take a cut in pay.

Answer:
Rick, Family