题目

For a moment nothing happened, then _____ all shouting together. A. voices had come       B. did voices come       C. came voices      D. voices would come 答案：C如图，正三棱柱所有棱长都是2，D棱AC的中点，E是棱的中点，AE交于点H.（1）求证：平面；（2）求二面角的余弦值；（3）求点到平面的距离.