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.

[Q]: Sentence1: Debra was looking for her cat. Sentence2: Sam said she'd help her. Sentence3: The cat was on a tree. Sentence4: Sam climbed up the tree but fell. Sentence5: The cat jumped down the tree.
[A]: Her cat, Sam, Debra

[Q]: 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.
[A]: Students, I (myself), Teachers, Mark

[Q]: Sentence1: Bob found a can on the ground. Sentence2: The can had no label. Sentence3: Bob had no can opener. Sentence4: He smashed and pounded, trying to get it open. Sentence5: He finally opened it to find delicious soup.
[A]:
Bob