单选题
Nowhere in nature is aluminum found free, owing to its always ______ with other elements, most commonly with oxygen. A. combine B. combined C. being combined D. having combined
【正确答案】
C
【答案解析】[解析] owing to是介词短语,后面应跟名词或动名词,its being combined with other elements为动名词短语。其他三个选项不合适,因为combine为原形动词,combined为过去分词,having combined为主动态。