Given the task definition, example input & output, solve the new input case.
In this task, you are given a question containing a blank (_) and two options. You should pick the best option to answer the question. Please answer with "A" or "B".
Example: Katrina gave Christine a stuffed animal for their birthday, but _ already had this one. (A) Katrina (B) Christine
Output: B
Since the blank is someone who received the gift and already had a stuffed animal, the answer must be "Christine".

New input case for you: Bob can either use his birth certificate or his driver's license as proof that he is a citizen. He chose the _ because it is large. (A) driver's license (B) birth certificate
Output:
B