nowhere in nature is aluminum found free ,owing to its always ___with other

题目

nowhere in nature is aluminum found free ,owing to its always ___with other
elements ,most commonly with oxygen A combined B having combiend C combine D being comebined 为什么选D 铝不是应该是主动跟其他物质结合的吗,因该是C啊

答案

选D
前面是its 而不是it,如果出现it ,也应该选Acombined ,因为it 是单数,要用一般现在时,也应该是combines
its being combined 是最合适的,要记住这种being 可以用以修饰名词,放在名词后,做后置定语