问题补充：
Many things impossible in the past are quite common today.
A. having being considered
B. considered
C. are considered
D. considering
答案：
A. having being considered
(答案→)B. considered
C. are considered
D. considering
解析：句意：很多在过去被认为是不可能事情在今天很常见。此空位于things后，与things之间是被动关系，故用过去分词做定语。having being considered 用做状语，不做定语，故排除A。are considered 是谓语动词形式，故排除C；considering是现在分词表示主动，故排除D。故选B。
