Teacher: 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 end sentence choices from (A) and (B), such that the story does not sound complete and coherent, i.e., select an incorrect end sentence.
Teacher: Now, understand the problem? If you are still confused, see the following 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.
Solution: B
Reason: As mentioned in fourth sentence, the incident turned a new leaf to Rick's life; so, he must be happy now. Also, he was previously in gang, so, this incident cannot make him to join a gang. So, B is incorrect.

Now, solve this instance: Sentence1: I decided to add a new fountain pen to my collection. Sentence2: I'd seen online videos of a nice pen called a Pelikan M800. Sentence3: So I went to the pen shop at my local mall. Sentence4: The shop had just the model of pen I wanted. 
 (A) I bought the pen. (B) I didn't buy the pen.
Student:
B