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？