Nowhere in nature is aluminum found free, owing to its always ______ with other elements, most commonly with oxygen.
A. being combined
B. having combined
C. to combine
D. combined
这道题的解析是owing to后要接名词或动名词,根据题意,此处要用被动语态,所以答案为A。但我的疑惑是,being combined可以完全看作一个名词吗?如果不可以,为什么她可以加在its的后面呢?如果是个名词,又为什么可以用always来修饰呢?always副词不是来修饰动词的么?