下列化合物中氧元素以游离态存在的有（）。
A.氧气
B.氧化镁
C.二氧化碳
D.四氧化三铁
参考答案：A
The wine industry in the area has developed in a special way, _____ little foreign ownership. [ ]
A. by
B. of
C. with
D. from
什么叫孤岛现象？孤岛的分类？
