题目内容：

having done和doing在句首的区别?
＿＿so many difficulties,the people in Wenchuan are still trying their best ti rebuilt their hometown optimistically.
A.Faced B.Having faced C.To face D.Facing
可以的话 分析一下每一个选项

优质解答

答案选B.
B 强调已完成
D 强调进行时
A 作句首表被动
C 表目的
句意是经历了这么多困难,汶川人民任然积极地全力重建家园
“了”字就提醒你要用完成时.