Given the task definition, example input & output, solve the new input case.
In this task, you're given four sentences of a story written in natural language. The given story is not complete and your job is to complete the story by selecting one of the sentence choices from (A) and (B), such that the story sounds fully coherent.
Example: Sentence1: Rick grew up in a troubled household. Sentence2: He never found good support in family, and turned to gangs. Sentence3: It wasn't long before Rick got shot in a robbery. Sentence4: The incident caused him to turn a new leaf. 
 (A) He is happy now. (B) He joined a gang.
Output: A
As mentioned in fourth sentence, the incident turned a new leaf to Rick's life; so, he must be happy now.

New input case for you: Sentence1: Bob got a rubix cube for Christmas. Sentence2: He struggled to solve the puzzle. Sentence3: Eventually, he was able to solve half of it. Sentence4: But, the full solution remained elusive. 
 (A) Bob worked hard and then finally solved the puzzle. (B) Bob then gave up on the video game.
Output:
A