將四個選項帶入原句中：
A.Having suffered such heavy pollution already,it may now be too late to clean up the river.
河流經(jīng)歷了如此嚴(yán)重的污染,現(xiàn)在再治理恐怕已為時過晚.
B.Being suffer such heavy pollution already,it may now be too late to clean up the river.
河流正在已經(jīng)遭到嚴(yán)重污染,現(xiàn)在再治理恐怕已為時過晚.
*使用了正在進(jìn)行時,然后還出現(xiàn)了“already”,搭配不當(dāng)
*suffer用法錯誤,和be搭配應(yīng)該是suffered
C.To suffer such heavy pollution already,it may now be too late to clean up the river.
河流為了已經(jīng)遭到嚴(yán)重污染,現(xiàn)在再治理恐怕已為時過晚.
*動詞不定式To do表示目的,“為了……”,原句的意思應(yīng)該不是“為了污染河流”
*“already”一般不和不定式搭配,一般用于完成時的,或者修飾狀態(tài)的
D.Suffered such heavy pollution already,it may now be too late to clean up the river.
河流已經(jīng)遭到嚴(yán)重污染,現(xiàn)在再治理恐怕已為時過晚.
***A和D選項：
兩個都對,A比D更好,所以選A.
A選項用了Having done,完成時非謂語動詞用在這樣的句子里面是帶有“因果含義”的
也就是說A選項Having suffered such heavy pollution already,it may now be too late to clean up the river.
因為“河流經(jīng)歷了如此嚴(yán)重的污染,”所以“現(xiàn)在再治理恐怕已為時過晚.”
D選項,僅僅是陳述了事實,采用了過去時,說明河流遭到嚴(yán)重污染,與主句“it may now be too late to clean up the river.”之間并沒有強(qiáng)烈的因果關(guān)系.
所以從這一角度來講,A比D更好.