First you can eliminate D because is shows nothing about whether the trip was fun.
While C shows they enjoyed the time, it could be 'what they needed' because it was relaxing or just an escape from reality. Not because it was incredibly fun.
A and B both show he most likely enjoyed the trip, but B is better because A still leaves room for questions. While in B you know that they enjoyed the trip because its directly said it was "the best trip ever", A he could be smiling because he's happy to see his dad or something else. B gives the most direct answer to the question.
