问题
选择题
_______ 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
答案
答案：A
句意为“这条河已经遭受如此严重的污染，现在要想清理也许为时已晚了”。suffer 发生在 clean up 之前，且有 already 暗示，无疑要用现在分词的完成式作状语。