So many representatives _______ , the conference had to be put o

So many representatives _______ , the conference had to be put off.
A、were absent
B、to be absent
C、being absent
D、had been absent
【正确答案】：C
【题目解析】：本题考查独立主格结构。句子后半部分的主干结构完整，句中有逗号但是没有连词，所以前半部分只能用非谓语动词。representatives与be absent是逻辑上的主谓关系且动作已经发生，所以后者应该为现在分词形式，此独立主格结构充当一个原因状语。