You are given a sentence, a question and two answer options ('A' and 'B'). Your task is to find the correct answer (return the string of the correct option, not 'A' or 'B') for the given question.
Q: Sentence: Bobby's grandparents have given him a box full of toys. They tell him to come pick the toys up in his wagon and pull the wagon home. The empty wagon is very light to Bobby, but once he puts the toys in it, he notices that it feels very weighed down. Question: In which situation will Bobby have more trouble getting the wagon to reach a quick speed from a stopped position? (A) when the wagon is empty (B) when the wagon is filled up with toys.
A:
when the wagon is filled up with toys