The correct answer is C. Studies have recently revealed that sinus infections in adults are more prevalent in the autumn than in the spring
Step-by-step explanation:
An objective tone refers to information that is delivered in a factual or objective way, this implies the information is true as it can be proved, also, objective tone implies the information or statements are neutral and unbiased which means personal judgments, feelings or opinions are avoided, as well as personal pronouns or similar that represent the judgment of an individual rather than facts. Additionally, formal language refers to complex or technical language used in written or spoken formal context.
The sentence Studies have recently revealed that sinus infections in adults are more prevalent in the autumn than in the spring uses an objective tone and formal language as the information is factual (proven by multiple studies) and it is not a personal judgment or opinion. Additionally, this sentence uses formal language including technical vocabulary such as "sinus infections" and "prevalent" and in a formal tone.