Even though the main source of________ exposure for a majority of the human population is the sun, the artificial tanning from sun beds contributes significantly to the total UV risk.
【正确答案】 C
【答案解析】解析：形近识别。ultraviolet紫外线的：ultraviolet light紫外线光。extra violent特别猛烈的；extra violet特别的紫罗兰；ultravirus超显微病毒。