Answer: The sentence that is an example of formal language is D. The Bugatti Veyron is the fastest and most luxurious car in the world.
Step-by-step explanation: Sentence D. is the only one that is written in a formal language since, unlike the other options, it does not include words that people use when they speak in a relaxed situation. Instead of resorting to the words "so", "totally" and "really" included in sentences A., B. and C., sentence D. makes use of superlative adjectives, such as "fastest" and "most luxurious", which indicate a formal usage of language. Moreover, unlike C., D. does not contain punctuation mistakes since it is made up of only one clause.