单选题 Nowhere in nature is aluminum found free, owing to it always ______ with other elements, most commonly with oxygen.

【正确答案】 A
【答案解析】非谓语动词题。owing to是介词，后应接名词或动名词，所以排除选项[C]和[D]。而根据题意，后面应该接被动语态形式，进而排除选项[B]。