Final answer:
Passepartout is furious at the delay because it might cost them the race.
Step-by-step explanation:
Passepartout is furious at the delay because it might cost them the race. In the passage, it is mentioned that they are participating in a race, and any delay can potentially be detrimental to their chances of winning. Therefore, option B, 'The delay might cost them the race,' is the correct answer.