题目

It's said that the power plant is now large as what it was. A . twice as B . as twice C . twice much D . much twice 答案：A将正方形ABCD沿对角线BD折成直二面角后，有下列四个结论：（1）AC⊥BD                     （2）△ACD是等边三角形（3）AB与平面BCD的夹角成60°   （4）AB与CD所成的角为60°其中正确的命题有 [     ]A．1个B．2个C．3个D．4个