When different cultures we often pay attention only to the differences without noticing

问题补充：

When different cultures, we often pay attention only to the differences without noticing the many similarities.

A. compared

B. being compared

C. comparing

D. having compared

答案：

A. compared

B. being compared

(答案→)C. comparing

D. having compared

解析：考查分词做状语。动词compare与句子we构成主动关系，就使用动词的现在分词。句意：当比较不同的文化的时候，我们通常总注意到它们之间的区别而没有注意到它们之间的相似之处。故C正确。