Which of the following sentences requires a citation?
A. Some sunscreens have an SPF of 35 or higher.
B. Any exposed skin is susceptible to sunburn.
C. One in five Americans will develop skin cancer by the age of 70.
D. Prolonged sun exposure can result in a burn.
This sentence presents a specific statistic that may not be common knowledge and is not the author's original idea, so it requires a citation to give credit to the source of this information. A citation is needed to show where this statistic came from, who conducted the study, and when it was conducted. Therefore, option C is the correct answer.
Therefore, the Correct Answer is C.