_______ such heavy pollution already, it may now be too late to

_______ such heavy pollution already, it may now be too late to clean up the river.
A、Having suffered
B、Suffering
C、To suffer
D、Suffered
【正确答案】：A
【题目解析】：本题考查分词短语作状语的用法。分词作状语，其逻辑主语必须是句子的主语，而本句的主语看似是it,其实它为形式主语，真正的主语为不定式，而不定式省略了逻辑主语for people，所以应用现在分词，又因already，应用完成时。