单选题   Everybody understands that the possibility always exists that the world champion may cheat in the game. The italicized part functions as a (n) ______ in the sentence.
 
【正确答案】 A
【答案解析】句子成分题。在整个句子中,that引导的句子对前面的the possibility起解释说明的作用,因此是同位语从句,故选A。