Answer: C). He has not ruled out rival explanations.
Step-by-step explanation:
A claim is a statement which is either based on some observation or evidences obtain from the experimental trials. Walter made a false claim as he didn't new the fact that the new car has more fuel efficiency so as the fuel retained the same amount as it was in the initially present in the car. Actually he has not ruled out the rival explanations and he cannot be considered as better driver.