题目

The new stadium being built for the next Asian Games will be______ the present one. A . as three times big as B . three times as big as C . as big as three times D . as big three times as 答案：B已知正方形ABCD的边长为2，E，F分别为BC，DC的中点，沿AE，EF，AF折成一个四面体，使B，C，D三点重合，则这个四面体的体积为______．