Final answer:
The word that best fits the blank in the given sentence is 'ambitious'. The correct answer is option d).
Step-by-step explanation:
The word that best fits the blank in the given sentence is ambitious. The sentence implies that the person's claims about making the city the best in the whole world did not seem credible or believable.
The word 'ambitious' suggests that the person's intentions or goals were lofty and grandiose, but lacked substance or evidence. In this context, 'ambitious' is the most appropriate word choice.